Are you seeing this issue on all machines and on all networks? Have you also verified that you're using the latest driver?
Have you found a resolution to this? I have seen it in the past but it has always corrected itself by doing the following:
- Right-click on the data source and select edit data source
- Within the data source editing window click on the server address
- Click OK
- Go back to visualization
- Right-click on data source and explicitly refresh
The only other thing I've done to get past it is to simply close Tableau and reopen. This is certainly not preferred though as you may have lost progress if it wasn't saved.