I don’t know if this is the same for you guys, but I was using WP-Translate, and got the same error you did after upgrading (actually, I had to rename the WP-Translate directory to deactivate it to get WP to work after teh upgrade).
The place that I got the error was in my footer, where I had added the code for the flags for the translator — I removed the code and the error went away (so JUST disabling the plugin wasn’t enough).
Unfortunately, I don’t know php well enough to know what call is missing or misinterpreted, so will wait for more folks to have problems with this plugin. ??
hope this helps.