Mvsckey Not Found Exclusive Fixed -

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The file (often read by emulators as part of the audio or core bios files) is the decryption key required to unlock and run the encrypted game data. If your emulator states that mvsckey or mvsc.key is missing, it means your romset is incomplete, outdated, or mismatched. Step-by-Step Fixes for MAME and MiSTer FPGA mvsckey not found exclusive

In IMS or CICS environments, control blocks may be protected by locks tied to storage keys. If transaction A holds an exclusive lock on key 5 and transaction B requests it, B receives this error. If B is a system task, it may trigger a dump. Navigate to -> Exclusions