Ok... Well this really looks like my mistake somewhere in the code, i don't have much corrupt files to test at (thankfully). Something like this definitely shouldn't happen with files created by Expander.

What version of Xtreme created that file? It may containt new records i havent encountred in my files so dont know about any problems with them.
Can you give me whole output? Output redirection to file can do the job: xar.exe -remove 2843 0 output.xar output1.xar > log.txt
That could help finding the problem.

I've been little too enthusiastic after that succesful conversion to xml
No idea whats the correct number to use, in fact the number may be even something different and be totally useles in this situation. That error message is not clear... just guessing :/ Maybe someone knows what exactly it means