How to load a DLL? (NSudoDM)

I'm trying to load a DLL (specifically NSudoDM), but I keep getting an error. Btw all you have to do with this DLL is load it, there are no functions to call in it.
Here's the code I've got for it:

  SetOutPath $INSTDIR

  File nsudodm.dll

  System::Call 'KERNEL32::AddDllDirectory(w "$InstDir")'

  System::Call 'KERNEL32::LoadLibrary(t "$InstDir\nsudodm.dll")p.r8'

  ${IfThen} $8 P= 0 ${|} MessageBox MB_ICONSTOP "Failed to load nsudodm.dll" ${|}

...
System::Call 'KERNEL32::LoadLibrary(t "$InstDir\nsudodm.dll")p.r8?e'
Pop $9
${IfThen} $8 P= 0 ${|} MessageBox MB_ICONSTOP "Failed to load nsudodm.dll, error $9" ${|} 

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