Check whether dll is 32 or 64 bit

Sn Path:C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin
C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin>CorFlags.exe D:\Source\Data\HelperUtility.dll

Download CorFlags Tool

To Determine the type of dll:
Any CPU: PE = PE32 and 32BIT = 0
x86 bit: PE = PE32 and 32BIT = 1
64-bit: PE = PE32+ and 32BIT = 0