The question everyone asks why should clear SPD Cache frequently. This is simple. Just to make sure that your client and SharePoint server environment both are in sync.
1.Close SPD and then remove all files from the following folder
C:\Users\AppData\Microsoft\Web Server Extensions\Cache
2.Go to %USERPROFILE%\AppData\Local\Microsoft\WebsiteCache and Clear all the files.
3.Restart SPD.
Happy Share Pointing :-)