zend_list_delete undefined symbol



I'm building a server and I configure/make/install
Apache-2.0.54
../configure --enable-so --prefix=/opt/apache2

mysql-standard-5.0.7

php-5.1.0b3
../configure  --with-mysql --with-apxs2=/opt/apache2/bin/apxs

WHen I start apache I get an error:
Cannot load /opt/apache2/modules/libphp5.so into server: /opt/apache2/modules/libphp5.so: undefined symbol: _zend_list_delete


Does anyone have an idea what this means and what I do about it.?

Al
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