[wp-hackers] fatal error on import

[fris]

Never got this before, got an error when trying to import posts from another
site, both 3.2.1 sites.

Catchable fatal error: Object of class __PHP_Incomplete_Class could not be
converted to string in wp-includes/formatting.php on line 1242

Line 1242 is

$value = stripslashes($value);

Of stripslashes_deep() function