Cannot open drawings getting error messages in C3D 2015

[1971jedwards407664]

In the last couple of weeks, we have been seeing otherwise good dwgs, coming up corrupted. We try to open them and we get a message "Drawing file is not Valid". When we try to recover the file we get an error stating "Unable to recover drawing file". We do use reference files and this has happened on two different projects. This might be a general CAD issue but since I am using C3D I thought I would post and ask for help here. Can anyone help me out? Thanks.

Jon

[rkmcswain]

Any change to the location where these drawing files are stored?
In other words, was there a server change recently?