Hello, sorry to reply a 3 month old thread, but this is exactly the same error I'm running into. Did you figure out what was the issue?

This doesn't occur in a clean installation, so there must be something unique in the environment, including the viewer, theme, configuration, etc. The nature of this specific kind of error begins with troubleshooting the view. The original post cites the issue being at Line 40.

https://hotcakescommerce....doesn-t-work-anymore

Hi Will,

You are correct. After a day and half of trial and errors, we narrowed down the problem relating to another vendor DNN module (DNNSharp/ActionForm). As soon as we removed the DLLs associated with that module from the BIN folder, the Category Viewer page works.

I'm going to reach out to their support, but if this is something that you've seen before, please do let me know too.

Thanks!
Wes

We don't use and we don't test against any of the DNN Sharp modules, so I'm not sure that we can help with that.

In the past, I've seen some of their modules change how DNN works and included numerous client-side libraries that aren't actually used on the front-end of the website, so their support is definitely the best next step for this. Sorry. :)