I had a similar problem back in the 1.4.7 versions of FTB.
My Fix:
1) Backup your world(s) to a different location.
2) Delete, download and re-install FTB
3) Make sure that FTB links to your relevant version of Java
- 64-bit OS = C:\Program Files\Java\jre7\bin\java.exe
- 32-bit OS =...