hi Pirx, when i worked with sw jams until a few years ago, there was an issue when the top value was higher than 256.
I have never known why but could work around it by just making new jams and inserting the bitmaps in these new ones.
In fact, I believe that the max height of a texture is also 256, otherwise it becomes corrupted.
Remember that a sw jam is only an 8 bit-color bitmap.
If you want, you can send me the sw jam (dirkholemans@telenet.be) and I'll have a look.
please include a little description what you wanna do exactly.
dirk