system.BadImageFormatException - while registering a cli.dll

I am trying to register the cli.dll in the GAC but I get the following error

The below exception is thrown in runtime .

Error occurred while initializing the installation :

System.BadImageFormatException: Could not load file or assembly of 'x_cli.dll' or one of its dependencies. is not a valid Win32 application. (Exception from HRESULT: 0x800700C1) .

Whenever , this dll is invoked in the code as well , this exception is always thrown.

Note: this dll was a working dll and had worked without any issues. I recently re-installed my windows 10 os and since then I am facing this issue.