After getting my gcw and only one week printf debugging I found the error!
It was in memcpy. I copied one byte to much. One byte in a memory area, which wasn't part of the destination field. So a random byte set to a random value.
Sometimes it crashed.
Sometimes the screen went lila.
Was VERY hard to find. -_-
However, here is the hopefully working version:http://ziz.gp2x.de/downloads/Sparrow-C4A-Manager/Sparrow-C4A-Manager-gcw-188.8.131.52.opk