I did the 2.9 upgrade on 10 sites, and I've got a handful that have the issue of the image upload not working. (ctype_digit() error)
I've double checked everything including required version types of PHP & mySQL and everything is as it should be. I re-uploaded all the files, twice, and double checked permissions.
The only solution I have found that works is here: http://wordpress.org/support/topic/347427 but that solution requires an wp system file be changed. I'm not comfortable with doing that because any future updates might result in the problem happening again or getting worse.
Can anyone shed some light on why I'm having the problem in the first place? I'm wondering if it is a server based issue because all of the affected sites are housed on two servers with the exact same configuration. The sites that *are* working are on a different type of server, unrelated to the two that aren't working.