Error was given when trying to make a SS with plenty of oil. Error corrected itself.

It appears that even though I purchased oil, and it showed in the war room as available oil, it took a few min before it was recognized enough to let me send the attack.

I have run into this also - it is like the error screen is cached and goes away if you do a page refresh.

next time this happens, try clicking the "refresh military" link below the "send attack" button and see if that solves the problem.

if it does, I'll code a refresh into the error code