Important:
Support for the old OneDrive for Business sync app with SharePoint Online has ended. If you see this 
Note: This article applies only to the previous OneDrive for work or schoolsync app (groove.exe). In most cases, we recommend that you use the newer OneDrive sync app (onedrive.exe) instead. Which OneDrive app?
Problem
When you use the Microsoft OneDrive for work or school (formerly Microsoft SkyDrive Pro) sync client to synchronize files between Microsoft SharePoint 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
Solution
To resolve this issue, reduce the number of lookup columns in the affected SharePoint list, and then try to synchronize the library. Do this until the error is no longer triggered. To delete a column, follow these steps:
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Browse to the affected SharePoint list.
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Click the LIBRARY tab on the SharePoint ribbon, and then click Library Settings.
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In the list of columns, click the name of the column that you want to delete.
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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.
More information
For more information about columns in SharePoint, see the following Microsoft websites:
Still need help? Go to Microsoft Community.
