I have the following problem when trying to install nsclient++ onto a Windows 2003 Server SP2 (note this is a member server).
Using a local administrator account on the server trying to install the install completes but the service does not get registered trying to manually register gives this error:
C:\Program Files\NSClient++\nsclient++ -install e NSClient++.cpp(212) Service installation failed: Unable to install service.5: Access is denied.
RESOLUTION
I ran “FileMon” tool from SysInternals which installing the service, and found access denied errors. But permissions where not the problem. It turned out that Sophos Anti-Virus thought the “Nsclient++.exe” was a virus. Once I authorised the nsclient++.exe file in Sophos the service could install and run fine.