I've been installing IBM Rational Software on and off for the past couple months - on my computer and a few others around the workplace; and I've never run into a problem like this.
The install files for several products are on a shared drive; when installing them with a FULL ACCESS Network Admin or Local Admin account.. I run into "failed to register X .dll" errors. Some software its only a few DLLs, others its 80+. It seems like some DLLs will register while others will not. Even using Regsvr32 to register them on the command-line fails. The software has been successfully installed in the past on multiple computers, however now this issue has come up on not only my computer but 2 others - both using the same admin access accounts as before.
I suppose its possible there may be file damage on the shared drive where the install files exist, but then why would the only issue during the install/uninstall be the registering/unregistering of DLLs. My only other guess at this so far has been that they are shared/protected DLLs from other Rational software, possibly of newer versions? Of course this may outline my total lack of understanding how Windows houses and manages DLLs.