Look at the link line and make sure all Lib library include files are in the correct location. Often you may not be using '-ldl' and have any required libs or problems with the database you are using.
If you connect to Apache 1.2.x, do you remember the additional information added to EXTRA_LIBS in the configuration file and rerun the Apache configuration file? Refer to the English INSTALL file for more information.
Some people replied that using '-ldl' and immediately following 'libphp3.a' to connect to Apache is the same.