Have you installed, initialized and restarted each Dogtag subsystem in the order they appear on the wiki?
Subsequent subsystems rely on certificates created prior to its installation.
Also – check your versions of mod_nss and nss – it will not work if you are using NSS 3.12 or later or MOD_NSS 1.0.7-3 or later. That is if you are using the prebuilt packages on the Dogtag wiki for Fedora 8 installation. I believe if you build locally from most recent source for 8, 9 or 10 it is ok.
Hope this helps.
Whereas i could install all other instances, but could not get going with pki-tps instance. What could be the common error. I have followed the same procedures for installing it. error message says 'unable to connect'.