Change the error message:
Portal_Log on terminator.beo-doc.de: Result of opening a TBX was not OK! More details in error log.
to
"Opening a TBX in termtagger '.$url.' was not successfull! More details in error log.".

In error log also the whole request content is logged.

Since no taskGuid is available in the context, no task info can be logged. This should not be necessary since, error does not block application progress and call to termtagger will be repeated.