Cant start Arma 2 OA or dayz

[aWalrus 0]

Whenever i try to start it it says data file to short c:\programfiles(x86) \steam\steamapps\common\arma 2 oa\expanion\characters_e.pbo'.Expected 673569908 b, got 334233600 b

please help me

[piemanpm 13]

Try deleting the file it's telling you is too short and then " Verify Integrity of game cache " of ARMA2:OA in steam

[aWalrus 0]

ok i did this and now the screen goes dark as if its gong to start but thn a new error comes up and says" error compiling pixel shader psspectacular Alpha:o

[piemanpm 13]

According to a few forum posts I've read. Run STEAM as Administrator.

[aWalrus 0]

i did this and it diddent change. im tring deleting entirely and reloading it. lets hope this works.

[aWalrus 0]

ok ive re downloaded bothn and now Arma2 wont work its says bad serial number given in setup