Most of the time we are in hurry and import mass transport requests in SAP server (through STMS_IMPORT) and unfortunately due to resource bottleneck , some TRs get hanged with IMPORT symbol. Though we wait for some hours with a hope , but it doesn't get through . So, in that scenario, you can check the following steps to get rid of that showstopper issue :-
You can check below option one by one and meanwhile you can check the TR queue status as all the steps are not mandatory to perform if any pre-step solves the issue ....
1. Delete the TR/ TRs (which are running with TRUCK symbol) from monitor (Press CTRL+ F8 in stms_import to check the list of TRs in monitor) .
2. Delete the TR entry through SE16N (in edit mode -> '&sap_edit' ) for all the TR/TRs from TRBAT, TRJOB, TMSTLOCKR tables.
3. Run RDDNEWPP report to schedule 'RDDIMPDP' job requires for TMS.
4. Terminate all the 'tp' processes running in OS.
5. Delete the TR line entries from <Target SID> file (open in notepad) available under /usr/sap/trans/buffer/. .
6. Still if you have issue in TR queue then check the logs under STMS_IMPORT > GoTo > tp System Log . Some time it shows that \usr\sap\trans\tmpD:\usr\sap\trans\tmp\<............<SID>> file is being used .......... waiting for 1 min . if you also get that log then delete the mentioned file from the corresponding location and check.
I am sure after following above steps, issue mentioned in the header will surely get resolved.