This file has been reported to be part of a spyware/malware/trojan. It is likely that the problem you are experiencing is linked directly to the spyware/malware/trojan rather than an actual missing DLL-file and the recommended course of action is to first locate/remove the Malware. We do not recommend downloading this file.
DLL-Files.com Support says:
This is a possible manual solution for you 'handyman-fixers' out there:
WARNING: Do this at your own risk. manually changing the registry could cause system critical errors if done incorrectly, the instructions below are not guaranteed to work on your particular system setup.
sp.dll and sp.reg is spyware that changes your IE explorer searchpage to a topsearcher.com portal that serves ads to your computer..
If there is a shortcut to SP.DLL, delete it.
goto the Startup tab,
Look for this line:
sp regedit -s C:\windows\sp.dll.
Uncheck that box and see if that fixes your problem.
search for SP.DLL (this action may take a very long time!)
Delete any reference
Goto Start>Find/Search>Files or Folders
Search for SP.DLL
Delete any results for SP.DLL