Errors when updating D6 - warning: array_pop() [function.array-pop]: The argument should be an array in /home/afterthe/public_ht

I have Googled and found many references to these two issues I am having but no solutions - so far (maybe I blinked and missed something)

When I upgraded from D5 to D6 I started having issues with Update.php -

<strong>Updating</strong>

An unrecoverable error has occurred. You can find the error message below. It is advised to copy it to the clipboard for reference.
Please continue to the error page
An HTTP error 404 occurred. http://example.com/update.php?id=1&op=do

warning: array_pop() [function.array-pop]: The argument should be an array in /home/afterthe/public_html/update.php on line 314.

The update process was aborted prematurely while running update # in .module. All errors have been logged. You may need to check the watchdog database table manually.

This stops me running the update - can anyone help?
Many thanks