The knowledge base entry gives the clue, I think, when it says it doesn't support encrypted/compressed folders.
What I have found is that newly created files of all types are fine. But if you change a file of a type that it does not understand, you will get an 8211 error and the file will not be backed up.
In my case, I have an app that creates a data file every day in a format that's indistinguishable from binary data. When new, these are fine - but if I ever go back and change one, boom. The same thing happens with compiled executables. The actual backed-up file seems to be fine, as you'd expect since it's just a collection of bytes.
The solution if this is a rare case, is to change the name or delete the backed up version. If it's more common, it's time to throw out the Maxtor software and take advantage of the configurable one-touch button action to run a real backup application. Like SyncToy 
.
Why the developers didn't just back up the file anyway, move the old versions down one in the history tree, and move on... I don't know. It doesn't seem to do anything that would justify trying to understand my file contents - back it up already!
