If an attempt is made to switch edit mode while the internet connection has dropped, the error message is:
Unable to parse content due to a Parsoid failure.
This is confusing, both for users who do know what Parasoid is and those who don't. The error message should indicate no internet connection, or unable to reach server, or similar.
Win7/Firefox. Reproducible: yes. Click reply. Type plaintext in VE mode. Drop internet connection. Try to switch to wikiedit mode.