I have a user that is trying to attach a file to an email but they are receiving an error message stating that the file has been shared too many times. This does not make sense to me.

Our Marketing team provides documents to our sales team that they share with their customers. We have a lot of sales reps which means it will likely be sent a lot,  We would prefer the sales team attach the file from Salesforce and not their desktop because there is consistency and version control through Salesforce. Also, if they upload from their computer there are likely multiple versions of the document floating around Salesforce. Can someone please help me understand why there is a limit to the number of times a file can be sent as an email attachment?