I've not heard of that error, that's crazy though I can't believe they don't list error codes. I've asked around and I can't find anyone with any information. This is one of those situations where even the Heidelberg help site doesn't have a listing.
Bizarre. When you call them you might want to let them know that the support web could use a bit of work. Sadly I am fresh out of ideas though.
Hey this is all I have found so far. Polar 115x Error codes 603 & 608 - Heidelberg Repair Forums
It appears to be a knife positioning error. I assume that turning it off and then back on again doesn't clear it. My old old 76 used to give me a problem that sounds like yours but no actual code. The blade wouldn't cycle .Heidelberg said it was due to a sensor for the knife position was going out and need to be replaced.They said it had to do with the timing of the blade reaching the sensor .The cutter didn't know where the blade was.We took the cover off of the back of the cutter to get to the timing box where the cams for the timing were located and sprayed them with contact cleaner.There may have been a cover on the timing box itself..I don't remember.
On the 76 that box was located on the back of the right side if facing the cutter.
We never did get heidelberg to come service it. It worked for several years like that and finally we got a new cutter.
Knife position error.
After start of cutting or during active cut, this message is output if the positions of electrical BDC and knife pulse counter are not plausible with respect to each other. In such a case, the knife movement is interrupted or not permitted, for safety
If the knife change was made correct, repare service with parts and knowledge is necessary.