My guess would be that "EmailReadMessages" does not actually complete on your home machine and that's when the underlying Java process shows up with the retrieval message. I'd check that in the debugger. If it does go to the next script step, check the return value of EmailReadMessages and/or Get(LastError).
I'm a little confused by your "Import" screenshot, though. I assume there is an import script step later in the script but I don't see the direct connection to EmailReadMessages.
As you suggested, limiting the number of emails might also help.