Since TPX 5.2 you can customize ACT-entries via TPXBATCH. When you try to update variable ACTLABEL with a 'Session Description' which contain blanks the job fails with messages "Close Parenthesis Required to End Parameter List" and "UNKNOWN COMMAND".
Here is an example of such a failing TPXBATCH-input:
UPDATE ACTAPPL (<acttable> <applid>
(ACTLABEL (Label containing several words)))
The Solution is to enclose the value for ACTLABEL into apostrophes:
(ACTLABEL ('Label containing several words')))
Now the TPXBATCH Job runs fine!