Check to see if the library libwebpayclient.so is missing any dependencies:
Use the following check to check the dependencies (correct the path to suit your environment):
ldd /usr/lib/php5/20090626+lfs/libwebpayclient.so
I had this same problem and discovered that libwebpayclient.so library has some precompiled dependencies on libssl.so.6 and libcrypto.so.6.
To work around this I just created some links to the current version of these files and everything worked (correct the path and library versions to suit your environment).
cd /usr/lib/i386-linux-gnu
sudo ln -s libssl.so.1.0.0 libssl.so.6
sudo ln -s libcrypto.so.1.0.0 libcrypto.so.6
Reference:
http://forums.whirlpool.net.au/archive/762312