'unable to load content [webcontrol name]. Please contact your systems administrator'
Finding Out What The Actual Problem Is
In order to get to the bottom of what was actually going on, I learned that I needed to modify my main web.config file which is located at:
to give me a more useful message.
1) First, I needed to modify the following line that begins with:
SafeMode MaxControls=”200” CallStack=”false” …
And change the CallStack property to “true”
2) Next, I needed to modify the following line:
customErrors mode=”On” /
And change the mode property to “Off”
3) Next, I needed to modify the following line:
compilation batch="false" debug="false"
And change the debug property to "true"
4) I then saved the the web.config file
5) Restarted IIS by executing the IISRESET command in the command prompt
6) Went through the steps of creating the web part page again.
7) I then received a far more useful error, with the first line of the error telling the story:
System.Web.HttpException: The file '/_layouts/ep/[webcontrol name].ascx' does not exist.
The Missing Step
Now knowing that the problem was that my control files didn’t actually exist where SharePoint expected them, I needed to locate the exact path where these files belonged. As it turns out, after searching, the “/_layouts/ep” path is not a physical path on the machine, so I had to find its physical location some other way. How I did this was searching the hard drive for another AX web part that was in the list of webparts that I verified was able to load (so I searched for “ActivitiesListAssociations”). This led me to the physical path of:
C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\12\TEMPLATE\LAYOUTS\ep
As expected, my custom web control files were not there.
So I copied the .ascx and .ascx.cs files from my project to this path, went through the steps to create the web part page, and web part finally loaded!