Sitecore 9 Installation - Could not load file or assembly 'ChilkatDotNet46'

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A collegue of mine was onboarding to a Sitecore 9 Update 1 project this week and had this error:

Could not load file or assembly ‘ChilkatDotNet46’ or one of its dependencies. An attempt was made to load a program with an incorrect format.

Ahh - this is an easy one, I thought, he just didn’t read the pre-requisites properly and forgot to install the Visual C++ 2015 Redistributable. I’m sure you will have read at this point that v9.0 update 1 introduced a dependency on this as it is needed by ChilkatDotNet46.dll.

So I helpfully pointed out that he should make sure all the pre-requistes should be installed!

Yeah... that would be great

But he had already installed the Visual C++ 2015 Redistributable on his machine. After some debugging and seaching around for the same error, the issue looked like it was a mismatch between 32 and 64 bit versions of the file.

Sitecore is requiring the 64 bit version of ChilkatDotNet46, but for some reason, ASP.NET was finding the 32 bit version. This post from Alex Brown (Could not load file or assembly ‘ChilkatDotNet2’ or one of its dependencies. An attempt was made to load a program with an incorrect format.) pointed us in the right direction, although he had the reverse issue.

It turned out that the application pool that was created for the Sitecore 9 instance, had Enable 32-Bit Applications turned on. But default, this is disabled. But for some reason (which we have not yet worked out), on 2 of my collegues machines, it was getting set to true for new application pools:

Setting the Enable 32-Bit

Once we disabled that setting, Sitecore came straight back up and we had no issues. So if you get that error, check your application pool settings and make sure that Enable 32 Bit Applications is disabled!

– Richard.