csvsys locked by another process

When executing a CSV sync, we sometimes get the following exception:

[1777292] Error connecting system (CSV Connector)!  [System.IO.IOException] The process cannot access the file 'C:\System files\XXX.csvsys' because it is being used by another process. 

This error occurs in about 10% of the sync runs and is not reproducible. 

Does anyone have any ideas about this?

Thanks

 Gregor