Flex Builder: An error has occurred. See error log for more details

How Many times have you encountered the problem while refreshing your flex builder or opening a mxml file?

• An error has occurred. See error log for more details.
• Unable to create this part due to an internal error. Reason for the failure: The editor class could not be instantiated.

I get this error more often. How I solve it?

Earlier I use to go to my workspace directory and delete the entire .metadata folder without knowing anything. In this way I used to lose all my settings.

Recently I have found a better way of solving this problem:

• I go to [workspace directory]/.metadata/.plugins/com.adobe.flexbuilder.codemodel/searchCache

• Backup the directories in there that end with “.index”. zip them up and keep them somewhere else
  
• Now delete the directories and keep the file “catalog.xml” file as it is there
• Run builder again and I should not get any error now
  

The problem is that the lucene index was corrupted or lost, probably during a failed Flex Builder shutdown. When flex builders starts it tries to load the lucene index but it fails to load that file and then it throws the error.