The once-per-year limit on IRA-to-IRA rollovers is a terrible trap for unwary taxpayers. It is ridiculously easy to avoid the trap--and ridiculously easy to fall into it. The IRS is sympathetic, but mostly it's helpless.
Here is the rule: If you receive a distribution from an IRA, you cannot roll that distribution over into any IRA if the distribution is received by you less than 12 months after another IRA distribution you received that you rolled over into an IRA. So says Internal Revenue Code Section 408(d)(3)(B).