As a SharePoint developer, you may be creating a web part and for the sake of testing you throw it up on your site. Then you decide to rename your class or get a new public key token for your class or something like that. After doing so, your page might stop loading with the following error.
You may not be a developer, you simply obtained a web part from another party and now it's not working and you get the following error.
An error occurred during the processing of . Could not load file or assembly 'Class.Class, Version=1.0.0.0, Culture=neutral, PublicKeyToken=20f2595270a5ec23' or one of its dependencies. The system cannot find the file specified
If you're lucky you are running into this on your default.aspx so clicking Go back to site doesn't work. If you want the fix, scroll down to The Fix. Or read on to understand what's going on.
In my own understanding, the issue is as follows:
When you add a web part to a page the web part's associated assembly is registered in the page, i.e.:
Screen shot from SharePoint Designer.
As you can see in lines 1 and 2, there are register tags for my two web parts I have on my page. The registers call on the entire assembly of the class the web part uses, which is what the page is erroring on. Normally, if you close a web part on a page through the web interface the web part doesn't get removed from the page, it's just invisible. In SharePoint Designer (SPD) the web part appears grayed out and the register tag remains on the page. Get SharePoint Designer for free!
To have the web part reappear, using SPD, change the __designer:IsClosed property of the web part from true to false. Save the page and your web part is back.
So how do we properly get rid of a web part? This is not the fix to the error, this is how to prevent receiving the error in the future. Instead of just closing the web part, you need to delete it.
To do so, go to Site Actions then Edit Page. Then click the Edit menu for the web part and you'll see Delete. Click to remove the web part, and it's registered tag from the page.
You won't need to do this for resident SharePoint web parts, like views of lists and libraries. This will be necessary for any third party custom web part.
The Fix
On to the fix. If it's too late for you, and the web part was already closed or removed or uninstalled and you're getting this error, try these steps:
- Go to http://servername/_layouts/settings.aspx. This should bring you to the Site Settings page.
- Click Reset to site definition in the Look and Feel column.
- Enter the full URL to the page that is erroring.
- Click Reset and confirm.
This functionality resets the page entirely so if you have any customizations on the page itself, it will remove them all. It does not appear however to remove other custom web parts that are installed.
I hope this helps!