Bulk Import Error Message

When using the eB Bulk Import utility I sometimes receive the following errors in the error log:

"Document: Failed to create document from the template in eB. Error: Transaction (Process ID 56) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.
Transaction (Process ID 56) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction."

Are you able to tell me why this may occur?

Rgds
Steve