SiteMinder's inability to load HTTPPLUGIN.DLL on a windows system can be caused by a variety of reasons.
Incomparable DLL's been placed in the windows system folders is just one of these reasons.
This problem can be caused due to the DLL search order windows utilizes.
By default windows performs the following search when trying to load any DLL
As the webagent folder is searched last, DLL files in the windows system folders override those installed by the webagent itself. If these DLL's are incompatible with SiteMinder the webagent will fail on startup.
To resolve this problem search for any DLL's that exist in both the one of the windows system folders (as listed in the summary) and the webagent's bin folder.
If a DLL exists in both places delete or rename the DLL that exists in the system folder.
Be careful to check all applications on the server after deleting these DLL's as an installed application may be dependent upon locating them in the system folder.
This problem is often caused by conflicting Comerr32.dll or k5sprt32.dll been present in the system32 folder.