[UnsafeControlException: A Web Part or Web Form Control on this Page cannot be displayed or imported

Question

When the upgrade of 2007 to 2010 took place i started to get errors for my webparts on my website as mentioned below: Error[1]

Web Part Error: A Web Part or Web Form Control on this Page cannot be displayed or imported. The type could not be found or it is not registered as safe.

Show Error Details

[UnsafeControlException: A Web Part or Web Form Control on this Page cannot be displayed or imported. The type could not be found or it is not registered as safe.]
  at Microsoft.SharePoint.ApplicationRuntime.SafeControls.GetTypeFromGuid(Guid guid, Guid solutionId, String assemblyFullName, String typeFullName, Boolean throwIfNotFound) 
  at Microsoft.SharePoint.WebPartPages.SPWebPartManager.CreateWebPartsFromRowSetData(Boolean onlyInitializeClosedWebParts) 

Answer 1

You need to add the web part type as safe control in the web applications "web.config" file and in the configuration > SharePoint > SafeControls section. The general format is like below:

Just replace AssemblyName, AssemblyVersion, AssemblyCulture, AssemblyPublicKeyToken, The class name of the web-part and The class name of the web-part with the information to your web-part.

Answer 2

This is usally shown very clear in the Trace logs. Check the LOGS directory on your front ends and search for the error.

Answer 3

Here you can find a step by step tutorial to track the error cause: http://www.bluedoglimited.com/SharePointThoughts/Lists/Posts/Post.aspx?ID=189