locked out of wp-admin / widget php error message

hello,

mediatemple decided to move my blog to another cluster.

Trying to reach wp-admin (or the blog index.php) results in this error message :

Warning: array_keys() [function.array-keys]: The first argument should be an array in /nfs/c04/h03/mnt/64847/domains/retiendra.com/html/wp-includes/widgets.php on line 1352

Warning: Invalid argument supplied for foreach() in /nfs/c04/h03/mnt/64847/domains/retiendra.com/html/wp-includes/widgets.php on line 1352

Warning: Cannot modify header information – headers already sent by (output started at /nfs/c04/h03/mnt/64847/domains/retiendra.com/html/wp-includes/widgets.php:1352) in /nfs/c04/h03/mnt/64847/domains/retiendra.com/html/wp-includes/pluggable.php on line 770

removing all themes except the default one did not change anything.

removing all plugins from the plugin directory did not change anything.

what should I do to revive my blog ?

Thanks in advance

Baudouin