[SOLVED] Error during auto save

When editing a post in Atahualpa 3.5.1 on WordPress 3.5.1 when the autosave activates I get the following error.

Catchable fatal error: Object of class CustomFields could not be converted to string in /home/eastero3/public_html/wp-includes/functions.php on line 1463

Has anyone seen this and have any ideas? I did make the "Auto Draft" change as mentioned in these forums but tried removing that change and turning off the Atahualpa Post Page Options to no avail. The page still get saved and looks fine from the front end.

Addendum: I saw a thread about the PHP version perhaps being an issue. That host was indeed set on PHP 4 but I just upgraded to 5 and the problem is still occurring.

2nd Addendum: When trying to add in image I get the following error in the modal image box.

Catchable fatal error: Object of class CustomFields could not be converted to string in /home/eastero3/public_html/wp-includes/formatting.php on line 433

Solution: After deactivating all my plugins the problem went away. I reactivated a few at a time but after all were reactivated the problem still had not returned. I can only surmise that the change from PHP 4 to 5 fixed the issue but needed a bit of time to "work"