You can try to decompile when Access complains that it cannot read the VBA project code. See Two answers to this SO question for detailed instructions: HOW to decompile and recompile .
If decompiling is not possible to restore the application in good working order, the fastest solution is likely to return to your last good backup.
If you want to make additional efforts to restore module changes since the last backup, check if you can all access the source code of the module. If the source code is readable, you can use the undocumented SaveAsText method to output the code to a text file:
Application.SaveAsText acModule, "Module1", "C:\SomeFolder\Module1.txt"
Then then load it into a new db file using the LoadFromText method.
Application.LoadFromText acModule, "Module1", "C:\SomeFolder\Module1.txt"
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