What causes "error performing X operation" messages?

[BethLott]

I have a REST service that I can query the feature class, but when I try to call addAttachment, or deleteAttachments, it returns error code 500 and the message "error performing <addAttachment or deleteAttachments> operation".  I am at a loss as to why this is happening, because I have an identical service on the same server that DOES allow adding and deleting attachments. The only difference is that the geo-databases are on different SQL Servers.

[BethLott · Accepted solution]

We never did figure out why these error messages were occurring. The GIS admin published a new service using the same map, but named it differently. Now it just works.