This is caused by two things:

• the arsenal uses "%ALL" as a magic string in the whitelists to mean "every item is whitelisted" (this is seperate from the 'full' mode that you get with ["Open",true] spawn bis_fnc_arsenal)
• If the whitelist contains a 'composite' weapon classname like "arifle_MX_pointer_F" this is converted to the base weapon (arifle_MX_F) and the attachments via bis_fnc_baseWeapon

Combine this and you get the following behaviour: Each entry in the weapons white-list is 'base-weaponified'. "bis_fnc_baseWeapon" does its work by looking up the config property "baseWeapon", however in order to do this it first needs to find the actual config. "%ALL" is obviously not a valid class inside CfgWeapons so bis_fnc_baseWeapon throws the error.

Since the presence of "%ALL" is already checked at some point in the whitelist parsing, the fix here would be to make sure that if the list contains "%ALL" the entire baseWeaponify logic is skipped. However it's a single RPT entry that doesn't cause any harm so it might just not be worth the effort to fix it :)

EDIT: Also seems like this is a duplicate of T78096