Unable to save PDF after esignature. "This file may be read only or opened by another user"

We've noticed a rise in employees unable to sign their time sheets in Adobe XI using the e-sign functionality. After signing and trying to save they get an error message that says "This file may be read only or opened by another user". There is no rhyme or reason here. Some times it will work. Others this error will occur. Some people never get the error. Some get it frequently. I've been able to delete the preference file for adobe and had some success. Others will notice the error come back after a while. They will download the pdf from their email as an attachment. The save location varies among users. Some save to their documents, some to the downloads folder and others on their desktop.

I've noticed that for some if we move the document from its original saved location it will work. But I have had an instance where a pdf required two signatures. Upon moving it into another location it allowed the first signature. But then we received the error on the second signature. We then had to move the document out of that folder back to its original location and it allowed the second signature.

I haven't been able to isolate a pattern because all experiences are different. And the fix that may have worked for one doesn't always work for the next.

I'm at a loss for what could be causing this issue and a loss for what will definitively fix it.

Users at my company are all running Mac OS X 10.11. The version of Adobe Acrobat i've noticed this issue occur is XI.