PHP 5.2.1 from sid or backports it not suitable for running sitebuilder.
If you really want to use php 5.2.1, you can try building it from the source and than manually configuring sitebuilder to use this PHP. You will also need new version of ioncube loader.
I just realized that one can't run SB 3.0.2 with php other than 5.1.x because SB includes binary php extension (sitebuilder3.so) that is linked with php 5.1
Originally posted by caustic I just realized that one can't run SB 3.0.2 with php other than 5.1.x because SB includes binary php extension (sitebuilder3.so) that is linked with php 5.1
As already was said that it's impossible for you to use PHP other than from 5.1.x branch. This is because you haven't sources of sitebuilder3.so binary library.