There is a KB article for this.
Resolution
1.Have all users log out of Sage 100 ERP
2.Open Custom Office, Utilities, Rebuild Customizer Log
A.Select the Module, User, and Company from the Log, click OK
3.Open Custom Office, Utilities, Update Custom Panels to Current Level
A.Keep all defaults, click OK to update
B.Print or Preview the Customizer Detail Report
If updating the customized panels does not work, the .lib/.M4L files may be corrupted.
Restore the ...\MAS90\xx\Custom folder from a backup created before the error occurred (xx = Module Code).
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