Tolerence for Budget in Internal Order

Hi

We have created a Internal Order for ABC for $6000 in FY 2012

goods received against this internal Order in FY 2012

Now when we are tying to post the invoice which is for (6000+25 (freight cost)

We are getting error 'avaliablity Control"

we have already carried forward the budget

Can someone tell me where I can check the tolerence for this order

I checked the same in the system ans it says

@ 90 % Waring

@ 110 % Error

why we are getting error for this

Any suggestion

Regards

Veenu