http://www.yetanotherforum.net/download . Is there a separate "Update" package? Also, are there recent instructions for updating YAF in DNN? We have the following instructions. Are these correct?

https://github.com/YAFNET/YAFNET-DNN/wiki/Installation-Upgrading 

The install package is also the update package for the dnn installation. The upgrade instructions in the wiki are still valid.

We proceeded with the upgrade of YAF in our DNN 9 environment today. We followed the instructions outlined in these documents.

https://github.com/YAFNET/YAFNET/wiki/Upgrade- (from-Version-1.9.5.5-or-above)
https://github.com/YAFNET/YAFNET-DNN/wiki/Installation-Upgrading 

We ran the upgrade from desktopmodules/yetanotherforumdotnet/install/default.aspx

However, we received the following error message:

Could not load file or assembly 'YAF.Types, Version=2.2.4.2, Culture=neutral, PublicKeyToken=null' or one of its dependencies. A strongly-named assembly is required. (Exception from HRESULT: 0x80131044)

We are no longer able to access our DNN environment now. We tried restoring all the DLLs from backup and the desktop module directories, however we continue to get the same error message. We did an IISReset but still have the same issue.

Do you have any idea what might be causing this?

Was the module Installation successful? It's possible that not all dolls where copied. Try to manually extract the dlls from the zip install package and copy the files over to the bin folder of the dnn installation.