This is a trivial issue, but since it took me a few seconds to realize my mistake / accident, I thought I would mention it.
I'm testing a .NET customization to the GL Transaction Entry window that monitors certain GL accounts that are entered in JEs. While entering a fake JE to test my customization, I chose a random GL account to balance the JE, and then clicked Save.
I received this message:
I was puzzled at first, but then I saw that the second line of the JE did not have a dollar sign in front of the Credit amount, and I had a pretty good guess what I had done.
The account I had randomly chosen, 600-9030-00, just happened to be a Unit account, not a Posting account.
Unit accounts can't be used to balance a GL journal entry, so my test JE was not balanced, as GP indicated.
This is presumably not a common mistake, and is one that is easily diagnosed and resolved, but since I almost never work with unit accounts, I thought I would mention it.
There are quite a few posts on unit accounts, such as these two from Boyer & Associates:
May your journal entries be balanced!