When QB Error 6006 Occurred
The main reason why the error occurs is due to the syncing QuickBooks company file does not match the installed QuickBooks version. The mismatch of versions of the QuickBooks accounting software is the root cause of this error.
How to fix the QB Error 6006?
For the rectification of this QB error 6006 you need to check if the QuickBooks installation is of the same edition. The editions are SimpleStart, Pro, Premier, Enterprise and Online as that of the syncing company file. You also need to make sure that you have the latest Intuit Sync Manager update. This is the possible and workable solution that is referred for resolving QuickBooks 6006 error completely.
If the all the above mentioned solution fail to resolve the QB error you can read the discussions and post messages and questions relating to your issue/error on free QuickBooks Community site introduced by Intuit or you can connect with the QuickBooks technical support for guidance and error fixation.