I m not pretty sure. However if the setting "NOSTOP" is given then it restricts mload from stopping if there is an error condition for variable-text length record. Check this setting. Secondly, we can use PAUSE ACQUISITION also. It will pause during the acquisition phase. You can kill the PID too if you know.
Just abort those sessions from Teradata Performance Monitor - if you've access OR ask your DBA to abort. Also you can grab the PID from UNIX box (from where you've run) and just kill the process. Don't forget to release mload on tables.