The mk4.zip file you have lacks the sub-file 461-mortal-k-4-25-u76.u76 . How to Fix It
Based on the syntax, the error is triggered by one of the following scenarios: 461-mortal-k-4-25-u76.u76 not found
2023-001
: MAME is frequently updated. A ROM set that worked on an older version of MAME might be missing files required by a newer version as more accurate hardware dumps become available. How to Fix "u76.u76 Not Found" Verify Your ROM Set Type The mk4
Are you seeing this on a (like an arcade machine) or a PC ? Did this happen immediately after a software update ? 461-mortal-k-4-25-u76.u76 not found