can't set iCloud Drive up

since downgrading to 10.10.2 after a recent freeze problem (see photo), i can no longer use iCloud Drive on my iMac.

it works great via the browser & iOS, just not via the finder - i'm presented with a spinning wheel for eternity. i've signed out/in to iCloud, restarted, etc.

our IT dept has asked that i do not update to 10.10.3 due to the problems i had previously.

any advice would be appreciated!

JB.