array merge error and can’t modify header problem error

Hey I just upgraded my wordpress to 2.7 and now I am getting load of errors. such as three of these with different arguments

Warning: array_merge() [function.array-merge]: Argument #2 is not an array in /wp-includes/capabilities.php on line 537

and two of these on different lines

Warning: Cannot modify header information – headers already sent by (output started at /wp-includes/capabilities.php:537) in /wp-login.php on line 255

and about 10 of these on different lines

Warning: Cannot modify header information – headers already sent by (output started at /wp-includes/capabilities.php:537) in /wp-includes/pluggable.php on line 676

any help I am totally lost and stuck here, thanks