Ajax error when viewing relationships under IIS and Joomla (HTTP400 - invalid syntax)
After months of struggling with this, I think I have solved it:  I found this article or others like it: https://stackoverflow.com/questions/8159321/request-exceeds-the-configured-maxquerystringlength-when-using-authorize which gave the parameters to tweak in web.config:


    
  

is an example.  As it is a private server I haven't spent much time optimising those parameters.