Customer cannot sign agreement due to "some miscellaneous error" occurring.

This is the first time my company has seen this particular error and we have obtained signatures of thousands of this exact document. On the customer's end, a red box that reads "Some miscellaneous error has occured" pops up with the agreement ID. 

The customer is accessing the document via the email we send. She is able to access the document with no issues, but is unable to sign for some reason. Thanks in advance for any help!