"View Redlines" and "Send for Negotiation" Errors
Clicking View Redlines or Send for Negotiation in Contracts for Salesforce produces either an Unable to compare selected documents or Your email message was not sent error.
The maximum number of OAuth authorization sessions was reached. Users can have no more than four OAuth authorization sessions working in a given environment. When a fifth session is kicked off, the first OAuth session is revoked.
It is also possible that the user who initiated the OAuth session was removed from the system.