Visio would display the following error when someone tried to check in a Visio file into a SharePoint 2010 Document Library:
Internal Error: #3400
Action 1787: Check in file
First try closing and reopening the file. Next try restarting Visio.
One of the fields in the document library had been set to required and as no data had been put into that field the file wasn’t able to be checked-in.
In this case we were able to set the field to optional.