ok - but it didn't do it before I upgraded so I'm guessing something else has changed. My guess is that it has something to do with usergroup permissions as per my other error thread - daily upload limits not working.
I use secondary usergroups extensively to give additional control - i.e., I have a primary usergroup Basic User and until they make a single post they cannot use the PM system. I have a secondary usergroup called pCanPM who's only purpose is to turn on the pm ability. My guess is that although this is set to No in Photopost it has 0 for upload limits and 0 for daily limit thereby allowing any size of file to be uploaded (and in fact one of the photos I uploaded was about 600k even though my limit should be 200k).
I think this is a flaw in the permissions system of Photopost. If Allow Uploads is set to No, the settings for that usergroup should not be used.
In the meantime, I'll remove unused usergroups from the photopost tables. Perhaps a future update would include the ability to do this from the front-end or allow more control over the 'refresh usergroups' option.