As discussed elsewhere in the forum and newsletter, look at your tax codes. Make sure each one is assigned to the correct tax liability account. Let us know if that fixes your problem.
OK yes this was one part of the issue. I imported the tax codes from the Manager website, but did not realize that they are not directly correctly assigned to the right liability account
But meanwhile I still get the server error now, though they are correctly assigned now
That points to a possible bug. There is some work going on with the general ledger engine that could be responsible. I will put this into the bugs category. Thanks for verifying that there is only one problem, not two.
What operating system are you using? I tried to duplicate this on a Mac. I got no error message. Instead, the program just quit.