More than likely something didn't go as well as you thought it did when you build php with solid db support.
try 'httpd -t' to see if apache tells you anything useful. Likely you might see something like "cannot load libphp4.so" or something about unresolved symbols.
Go back to your php directory, try this:
./configure --with-solid=/usr/local/solidSDK351/Linux_glibc2 |tee config.log
and let it run. Then, try this:
grep -i solid config.log
and see if support for solid really got built or not.
If it did, then it could be something as simple as shared libraries not having a parth library in /etc/ld.so.conf, to fix that, just figure out where the solid libs live, and add a line to /etc/ld.so.conf with that path in it, and run ldconfig (do all this as root, of course) and then it should work.
