Sharepoint Designer doesn't allow to open the Custom List Form(.aspx) file in Design view.

Scenario.

         When attempting to modify a custom list form in SharePoint Designer, the form never displays in design view. There is no error message, no edit window tab.




Resolutions :

We need to clean up the user profile using these steps:

1. Close SharePoint Designer 2007.
2. Clear your Internet Explorer's temporary Internet cache.
3. Open My Computer and go to %System Drive%\Documents and Settings\%user%\Local Settings\Application Data\Microsoft\WebSiteCache (If you are running Vista, that path is different - look for %System Drive%\Users\%user%\AppData\Local\Microsoft\WebSiteCache).
4. Go to a directory that looks similar to the name of the website you were connecting to.
5. Delete the assembly with the name of your SharePoint Site.
6. Type %temp% at a run prompt and delete all the temp files in there.
7. Delete the contents of: C:\Documents and Settings\username\Application Data\Microsoft\Web Server Extensions\Cache.