Error after passing WP2.7 to php5

After functionning properly under my Bluehost provider’s default setting of php 4.49, my main WP 2.7 site now generates an error message after switching to php5 via the provider’s control panel.

The error message is: “Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 71 bytes) in /home4/xxxxxx/public_html/oustal/wp-includes/gettext.php on line 91”

I can of course no longer access this site’s WP login and CP and have placed the site temporarily offline with an index.html file pending resolution of this problem.

However another former WP 2.7 beta test installation in another subdirectory is working properly, as are several WP sites with pre-WP 2.7 installations.

Any advice is eagerly accepted.
Many Thanks