GAO Statement that Agency Legal Advice Not Sufficient

Is anyone aware of a GAO decision re: appropriation availablilty where GAO stated that obtaining agency legal opinion wasn't sufficient to avoid liability for an action because GAO makes themselves available for appropriation decisions before an agency takes action? I've searched at length re: this issue and have been unable to find it, but I read that in some GAO document over the last year or so (although the document may be more than a year old).

Any assistance is much appreciated!

Thanks,

Mike