Are you using the most recent version of Tableau Desktop (7.0.13)? If not, I would recommend upgrading.
If this does not solve the issue there are a couple of other things to try before contacting our support team.
1. Do you have any firewall or antivirus products that may be potentially interfering with the Tableau Data Engine communication? If so, try disabling them when creating the extract.
2. Do you have the latest driver for you MySQL database? http://www.tableausoftware.com/support/drivers
If none of these resolve the issue, I would recommend sending a ticket to our support team at email@example.com with the following information:
1 - Screenshot of the error along with "Show details" information, if available
2 - What kind of an extract is attempted - full/incremental?
3 - Version of MS SQL in use
4 - Date and time of the issue
5 - Tableau Desktop log files (see http://www.tableausoftware.com/support/knowledge-base/sending-tableau-desktop-log-files for instructions on bundling and sending the log files)
Yes we're using the latest Tableau and latest MySQL drivers.
I'll send the details right now.
The bug has disappeared in Tableau 8