Nsis Vista codecs not being registered on install

I have a nsis script that installs 2 .dll video codecs to the windows\system32 directory, then registers them before finishing. It is working fine in XP but Vista is not getting the codecs registered.

CopyFiles /SILENT "$INSTDIR\ir50_32.dll" "$SYSDIR\ir50_32.dll"
CopyFiles /SILENT "$INSTDIR\ir50_lcs.dll" "$SYSDIR\ir50_lcs.dll"
RegDLL "$SYSDIR\ir50_32.dll"
RegDLL "$SYSDIR\ir50_lcs.dll"
Delete "$INSTDIR\ir50_32.dll"
Delete "$INSTDIR\ir50_lcs.dll"

Why wont this work on vista?

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