3793905 - RC=12 on Import Request Piece List without any error message

When importing a request, the request ends with errors on Import Request Piece List and if you try to find a more detailed error message, nothing is found. 

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 Import of object list of a request
 Transport request : <SID>K<NUMBER> 
 System : <SID>
 tp path : tp 
 Version and release: <version> (Patch level: <patch>) 916

 Import of object list of a request
 End date and time : <date and time>
 Ended with return code: ===> 12 <===
 ######################################

A message similar to this one below might be found on SLOG:
ERROR: stopping on error 12 during CMDIMPORT

SAP Netweaver

MT_MODE, AUTO, TMS, transport, RC=12, import request piece list,  , KBA , BC-CTS-TMS , Transport Management System , Problem