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Does it convert any file or just the "large number" of files. If it doesn't convert any files then reinstall Prime and the converter. If it is specific files then look at functions in the file that may not be converting.
Same issue - "Errors during conversion xmcd files to Prime": https://community.ptc.com/t5/Mathcad-Installation/Errors-during-conversion-xmcd-files-to-Prime/td-p/758507