Could not load file or assembly. An attempt was made to load a program with an incorrect format (System.BadImageFormatException)

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1. You pretty sure,  you're having a 32-bit / 64-bit conflict. It sounds like your main project might be set to 32-bit while the class its referencing is set to 64-bit.

IIS >> Select Your Project >> check Application pools >> 

     IIS >> Application Polls >> Select Application pool of your project >> Advanced Setting >> Under general tab : Enable 32-bit applications -True

2. Assembly manager loaded from: C:\Windows\Microsoft.NET\Framework64