Got this error after creating some taxonomy fields and then importing them into Visual Studio using CKSDev. If I then tried to connect a term to the taxonomy field the error occured.

 (“The object has been updated by another user since it was last fetched”)

This did not happen at first, but only after removing my Development Site Collection, and then deploying again from Visual Studio to a new clean sitecollection.

The error was thrown because there was a version number specified in the field xml of the taxonomy field. More detailed information can be found at: http://www.mpspartners.com/2012/02/SharePointTaxonomyFieldandTheobjecthasbeenupdatedbyanotherusersinceitwaslastfetched/