Checked this morning, and the Celestrak server is working fine. The usual problem with downloading is a firewall which needs an exception to permit SATPC32 to access the Internet. If your program was downloading, and now isn't, I would still check the firewall for blockage. If all else fails, cut the URL from the Celestrak.SQF file and paste it into the URL window of your browser. You should get the desired file, which you can save as a text file, and then copy it to the Kepler directory. Make certain you get the right directory. It will be something like
C:\Documents and Settings\WA4SCA\Application Data\SatPC32\Kepler
There will be other Kepler directories, but they are for backup and default data.
Let us know the results.