I am lost - Dependency madness (RHEL53)

Just thought to check 'yum update' for no apparent reason ...
Suddenly I get hit by a wave of
The list goes on and on ... always referring to libpng12.so.0
Now the file is there (not just once even):
Any tips for a n00b ?
Some people suggest this is related to either 'zlib' or 'glibc'
But
I am lost
Edit:
Mmm... I am wondering if rpmforge installed versions which don't yet exist in the RHEL repo .. I excluded 'libpng.i386' now from yum and I can update again *headscratch*
Suddenly I get hit by a wave of
Error: Missing Dependency: libpng12.so.0 is needed by package netpbm-progs-10.35-6.1.el5_3.1.i386 (installed)
Error: Missing Dependency: libpng12.so.0(PNG12_0) is needed by package ghostscript-8.15.2-9.4.el5.i386 (installed)
Error: Missing Dependency: libpng12.so.0 is needed by package kolourpaint-1.2.2-2.el5.rf.i386 (installed)
Error: Missing Dependency: libpng12.so.0(PNG12_0) is needed by package compiz-0.0.13-0.37.20060817git.el5.i386 (installed)
Error: Missing Dependency: libpng12.so.0 is needed by package 2:pilot-link-0.11.8-16.i386 (installed)
Error: Missing Dependency: libpng12.so.0(PNG12_0) is needed by package zvbi-0.2.33-1.el5.rf.i386 (installed)
The list goes on and on ... always referring to libpng12.so.0
Now the file is there (not just once even):
[[email protected] lib]# locate libpng12.so.0
/usr/NX/lib/libpng12.so.0
/usr/NX/lib/libpng12.so.0.1.2.8
/usr/lib/libpng12.so.0
/usr/lib/libpng12.so.0.10.0
/usr/lib/vmware/installer/lib/lib/libpng12.so.0
/usr/lib/vmware/installer/lib/lib/libpng12.so.0/libpng12.so.0
/usr/lib/vmware/lib/libpng12.so.0
/usr/lib/vmware/lib/libpng12.so.0/libpng12.so.0
Any tips for a n00b ?
Some people suggest this is related to either 'zlib' or 'glibc'
But
[[email protected] lib]# rpm -qa |grep zlib
zlib-1.2.3-3
[[email protected] lib]# rpm -qa |grep glibc
glibc-headers-2.5-34
compat-glibc-2.3.4-2.26
glibc-2.5-34
compat-glibc-headers-2.3.4-2.26
glibc-common-2.5-34
glibc-devel-2.5-34
I am lost

Edit:
Mmm... I am wondering if rpmforge installed versions which don't yet exist in the RHEL repo .. I excluded 'libpng.i386' now from yum and I can update again *headscratch*
My own knowledge base made public: http://open902.com 

Comments
I already rebuild the rpm database if this is what you mean
Edit yet again : I was sure I tried that ... but MAYBE I tried that on the test server for testing *oops* - now tried it again on my workstation and now I don't get the dependency error anymore. Now when I include libpng again in yum it actually updates it
Yay ...