The Metal Slug Anthology SLUS-21550 error is because the old pnach system enable all the cheats and broke the game.
In the new pnach format for the lnew qt versions you can enable the cheats after you start the game and enable only the cheats for the metal slug game you are playing.
Pnach for the new format:
[Cheats/Metal Slug 1 P1 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,0182437E,extended,00000065
[Cheats/Metal Slug 1 P1 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,118244CA,extended,0000FFFF
[Cheats/Metal Slug 1 P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,018244C9,extended,00000063
[Cheats/Metal Slug 1 P1 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,0182448C,extended,000000FF
[Cheats/Metal Slug 1 P2 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,0182441E,extended,00000065
[Cheats/Metal Slug 1 P2 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,1182456A,extended,0000FFFF
[Cheats/Metal Slug 1 P2 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,01824569,extended,00000063
[Cheats/Metal Slug 1 P2 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000000
patch=1,EE,0182452C,extended,000000FF
[Cheats/Win] Metal Slug 2
[Cheats/Metal Slug 2 P1 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,0192527F,extended,00000063
[Cheats/Metal Slug 2 P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,01930351,extended,00000063
[Cheats/Metal Slug 2 P1 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,11930354,extended,0000FFFF
[Cheats/Metal Slug 2 P1 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,0192551E,extended,000000FF
[Cheats/Metal Slug 2 P1 Infinite Vehicle Cannon]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,019328A8,extended,00000063
[Cheats/Metal Slug 2 P1 Infinite Vehicle Energy]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,019328A3,extended,00000030
[Cheats/Metal Slug 2 P2 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,01925327,extended,00000063
[Cheats/Metal Slug 2 P2 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,01930350,extended,00000063
[Cheats/Metal Slug 2 P2 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,11930356,extended,0000FFFF
[Cheats/Metal Slug 2 P2 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,019255C6,extended,000000FF
[Cheats/Metal Slug 2 P2 Infinite Vehicle Cannon]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,019328CC,extended,00000063
[Cheats/Metal Slug 2 P2 Infinite Vehicle Energy]
patch=1,EE,D1FFCF9C,extended,00000001
patch=1,EE,019328C7,extended,00000030
[Cheats/Metal Slug X P1 Infinite Metal Slug X P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,01925291,extended,00000063
[Cheats/Metal Slug X P1 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,1193072C,extended,0000FFFF
[Cheats/Metal Slug X P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,01930729,extended,00000063
[Cheats/Metal Slug X P1 Invincibility You can still die in vehicles]
patch=1,EE,E0020002,extended,01FFCF9C
patch=1,EE,0192552A,extended,00000040
patch=1,EE,01925550,extended,000000FF
[Cheats/Metal Slug X P2 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,01925341,extended,00000063
[Cheats/Metal Slug X P2 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,1193072E,extended,0000FFFF
[Cheats/Metal Slug X P2 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,01930728,extended,00000063
[Cheats/Metal Slug X P2 Invincibility You can still die in vehicles]
patch=1,EE,E0020002,extended,01FFCF9C
patch=1,EE,019255DA,extended,00000040
patch=1,EE,01925600,extended,000000FF
[Cheats/Metal Slug X P2 Infinite Vehicle Energy]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,0193064C,extended,00000030
[Cheats/Metal Slug X P2 Infinite Vehicle Cannon]
patch=1,EE,D1FFCF9C,extended,00000002
patch=1,EE,01930652,extended,00000063
[Cheats/Metal Slug 3 P1 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,01D84342,extended,00000064
[Cheats/Metal Slug 3 P1 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,11D92B82,extended,0000FFFF
[Cheats/Metal Slug 3 P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,01D92B7C,extended,00000063
[Cheats/Metal Slug 3 P1 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,01D84608,extended,000000FF
[Cheats/Metal Slug 3 P2 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,01D843F2,extended,00000064
[Cheats/Metal Slug 3 P2 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,11D92B90,extended,0000FFFF
[Cheats/Metal Slug 3 P2 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,01D92B8A,extended,00000063
[Cheats/Metal Slug 3 P2 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000003
patch=1,EE,01D846B8,extended,000000FF
[Cheats/Win] Metal Slug 4
[Cheats/Metal Slug 4 P1 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000004
patch=1,EE,01B84B10,extended,00000064
[Cheats/Metal Slug 4 P1 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000004
patch=1,EE,11B92E7A,extended,0000FFFF
[Cheats/Metal Slug 4 P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000004
patch=1,EE,01B92E74,extended,00000063
[Cheats/Metal Slug 4 P1 Invincibility]
patch=1,EE,E0020004,extended,01FFCF9C
patch=1,EE,01B84D9E,extended,00000040
patch=1,EE,01B84DC8,extended,00000057
[Cheats/Metal Slug 4 P2 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000004
patch=1,EE,01B84BC0,extended,00000064
[Cheats/Metal Slug 4 P2 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000004
patch=1,EE,11B92E8A,extended,0000FFFF
[Cheats/Metal Slug 4 P2 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000004
patch=1,EE,01B92E84,extended,00000063
[Cheats/Metal Slug 4 P2 Invincibility]
patch=1,EE,E0020004,extended,01FFCF9C
patch=1,EE,01B84E4E,extended,00000040
patch=1,EE,01B84E78,extended,0000006B
[Cheats/Metal Slug 5 P1 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,01B24A48,extended,00000064
[Cheats/Metal Slug 5 P1 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,11B31464,extended,0000FFFF
[Cheats/Metal Slug 5 P1 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,01B3145E,extended,00000063
[Cheats/Metal Slug 5 P1 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,01B24D50,extended,000000FF
[Cheats/Metal Slug 5 P2 Infinite Lives]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,01B24B0C,extended,00000064
[Cheats/Metal Slug 5 P2 Infinite Arms]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,11B31474,extended,0000FFFF
[Cheats/Metal Slug 5 P2 Infinite Bombs]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,01B3146E,extended,00000063
[Cheats/Metal Slug 5 P2 Invincibility]
patch=1,EE,D1FFCF9C,extended,00000005
patch=1,EE,01B24E40,extended,000000FF
[Cheats/Metal Slug 6 P1 Infinite Lives]
patch=1,EE,012FB4FF,extended,00000064
[Cheats/Metal Slug 6 P1 Infinite Arms]
patch=1,EE,112DA5C8,extended,0000FFFF
[Cheats/Metal Slug 6 P1 Infinite Bombs]
patch=1,EE,012DA5C5,extended,00000063
[Cheats/Metal Slug 6 P1 Invincibility]
patch=1,EE,012DA588,extended,00000064
[Cheats/Metal Slug 6 P2 Infinite Lives]
patch=1,EE,012DADB7,extended,00000064
[Cheats/Metal Slug 6 P2 Infinite Arms]
patch=1,EE,112FB1D0,extended,000003E7
[Cheats/Metal Slug 6 P2 Infinite Bombs]
patch=1,EE,012FB1CD,extended,00000063
[Cheats/Metal Slug 6 P2 Invincibility]
patch=1,EE,012FB190,extended,00000064