I take it you are on windows.
- Close down the vipcoin client
- Go to C:\Users\{you user}\AppData\Roaming\
- Make a backup of the vipcoin folder(in case you delete too much)
- go to the vipcoin folder
- Remove everything inside the folder except: peers.dat, wallet.dat and vipcoin.conf
- open the vipcoin client and let it re-download the blockchain