I was able to use the Creation Kit for a few hours (I only started recently) but now whenever I tried to use it I get an instant crash. I have verified the integrity of the game cache which didn't solve the issue, I have reinstalled the CK, I have deleted all local content (through steam) and re-installed it. I have a couple of mods I was working on so a fast reply would be really appreciated, thanks.

If your trying to load a mod with multiple master files, then you need to tweak the ini file

• By default, you can only load either Dawnguard, Hearthfire, or Dragonborn data into the CK, but not all at the same time. To load multiple masters, in SkyrimEditor.ini, add bAllowMultipleMasterLoads=1 under the [General] heading.

http://www.uesp.net/wiki/Skyrim:Creation_Kit

Sorry I forgot to mention I have already done that. Anyway it crashes before I am even able to select which master files to load.

You also need to find the SResourceArchiveList2 line and make sure the BSA files for each DLC are listed there.