What I find real odd, is that an SE version would require you to enter a serial number. These are provided to vendors in lots, and the serial numbers if required are embedded in the installation, thus not requiring manually entering it. Most of the time when you try to register an SE version with Corel or Ulead, you will get the error message that it has already been registered. The reason is that Corel or Ulead records those SE versions' registration when it "sells" them to the vendors.
Like John stated I would be contacting your "reputable vendor" about this. Hopefully they are reputable and try to correct this.
Ron Petersen, Web Board Administrator