Steam wants to download Skyrim again, but runs ok on SKSE?

[ishamm]

I have been running skyrim fine, until today, i opened steam, and it immediately started 'updating' skyrim (actually re-downloading the whole game i guess, since its 8gb, but it says updating)

 

i dont know whats caused this, since the files are all still there, and the game runs fine through SKSE on NMM.

 

I would quite like to get this sorted, not least as its stopping me trying out the 1.6 beta! XD

 

any help would be much appreciated