I had the same problem, it's incredibly annoying and there's strangely little posted about it on the interwebs. Anyway, here's how you fix it: Goto File in the upper left hand corner, then Options > Trust Center > Trust Center
Settings > Privacy Options > then un-check the check box that says "Remove personal information from file properties on save", then hit OK. Hope that helps.
This isn't a fix, it just hides the problem.
The dialog is not an "Error", it is an "Informational" message, which is less severe than an error. It just says there "MAY" be personal information in the file. That is pretty useless, is there is there not personal info. Who would know better, MS has
the inside info to be able to tell us. This is another fine example of a half-assed effort. MS could tell us exactly what and where this alleged personal information is, but they are too lazy to do it right.
Disabling the informational warning does nothing to remove the personal information, if it is there.