Quoting wa7eth@frontier.com who wrote on Wed 2014-08-27 at 00:15:
I am having difficulty with SATPC32 tracking the ISS accurately. All other satellites appear to track OK but the ISS is way off compared to several web based tracking sites. I would appreciate any tips on how to troubleshoot this problem. Please respond off the AMSAT-BB to WA7ETH@frontier.com
Have you updated your TLEs recently? I noticed a few times predictions of ISS can be way off in gpredict/amsatdroid and it was always fixed when I updated the TLEs.
My theory is that this is due to the corrections the ISS makes to stay at the right height and avoid space debris which makes it less predictable than amateur satellites that just stay in orbit and can't correct their course. I am open to corrections on this theory.
Koos van den Hout