When you use the Microsoft OneDrive for Business (formerly Microsoft SkyDrive Pro) sync client to synchronize files between Microsoft SharePoint Online and Windows Explorer, you receive the following error message:
We couldn’t sync this library.
When you click Technical Details in the error window, you receive the following message:
The query cannot be completed because the number of lookup columns it contains exceeds the lookup column threshold enforced by the administrator.
Error code=0x80070093; Error source=Groove
To resolve this issue, reduce the number of lookup columns in the affected SharePoint Online list, and then try to synchronize the library. Do this until the error is no longer triggered. To delete a column, follow these steps:
Browse to the affected SharePoint Online list.
Click the LIBRARY tab on the SharePoint ribbon, and then click Library Settings.
In the list of columns, click the name of the column that you want to delete.
Click Delete at the bottom of the Edit Column page, and then click OK.
NOTE: Before you delete a column, consider how this might affect the list.
For more information about columns in SharePoint Online, see the following Microsoft websites:
Still need help? Go to Microsoft Community.