Dealing with with infinite form loading (spinner) in large customizations

One of the most common issues in BPC PowerForms is the never-ending loading indicator display, with the form not being able to load at all. This is accompanied with a generic "Error 500" that is thrown in the browser's developer tools console, as well as the "Network" tab (if you press F12/Developer Tools), and it's encountered only in large form customizations (with many controls or scripts). If you notice that the issue doesn't happen in a new list that has only a couple of fields, then most probably the resolution below fits your scenario.

The most frequent reason for this behavior is that SharePoint/ASP .NET by default prevents large JSON streams from being serialized. Therefore you will have to allow a larger number of bytes (that’s why it happens only in customizations of a certain size and above) in your web.config file of your SharePoint web application:

<system.web.extensions>

<jsonSerialization maxJsonLength="5000000" />

</webServices>

</scripting>

</system.web.extensions>

Normally the web config entry should be there, but there are numerous cases in Sharepoint installations (especially in 2013/2016 systems) where the configuration section is missing.

You should apply this change with caution to every web front end of your SharePoint farm.