I had an oddity reported by a client just after an upgrade from Microsoft Dynamics GP 10 to Dynamics GP 2013 R2. After opening Enter/Match Invoice, entering the header information and clicking Auto-Invoice they received the following error:
Microsoft Dynamics GP
You must close the Select Purchase Order Items window before continuing.
I connected to their system and attempted to reproduce the error. My first few attempts failed and everything worked as expected. However, the problem did finally occur and I was able to see the problem happen a few times although it took a few minutes for me to realise the pattern.
The error message appeared when the cursor was in the lines scrolling window; if the cursor was still in a header field the error was not produced.
I have tested this on some of my test systems and the error appears to have been introduced between Dynamics GP 2013 SP2 and Dynamics GP 2013 R2.
The workaround is to make sure the cursor is not within the lines of the scrolling window and this message won't appear.