I know this is a really old question but for those people who may come across it. The most common reason for this error today is the end user getting the error using a new computer.
There is a difference between REFRESHING the data Provider and entering the Query Panel and Re-Running the report. REFRESHING takes the same SQL and re-runs it against the same connection that was used last. If they are using a new computer the report is trying to use the network path of the old PC.
Resolution: Re-entering the Query Panel will rebuild the SQL picking up any changes and it will run against the current Universe/User connection.