Full Error Message: 
“Unable to Access Page. The value of the “p3_lkid” parameter contains a character that is not allowed or the value exceeds the maximum allowed length. Remove the character from the parameter value or reduce the value length and resubmit. If the error still persists, report it to our Customer Support team. Provide the URL of the page you were requesting as well as any other related information.”

-This error can happen when document action is set for email functionality though there may be a restriction placed on the object in use.

How to resolve: 
1. Make sure the ‘Allow Activities’ is turned on the custom object or whatever base object you are using in document action. If you do not have this turned on, you wouldn’t be able to send emails from the record.

2. You can also check that the “Document Action” custom object is not set to private. You can review the access to objects by going to Setup >¬†Security Controls > Sharing Settings > Find Document Action custom object > click to edit and change to public or modify from the “private” setting if needed.