liudr:
I guess the size limit is more for pads than for traces. Yes, I drew the ground plains within 80mm limits but I do need some extra board space to put 2 mounting holes and some space for text on silk screen. Thanks.
Eagle's funny that way. While it allows you to draw the dimension layer as large as you want, it will not allow components to be placed outside of the limitations of whichever version you have. So you can create a 80mm x 100mm board but draw the dimension as 100mm x 100mm. When you tell Eagle to autoroute, it will gladly assume that you can use that additional 20mm, after all, you drew the dimension that way. Also, the fab house will make your board based on that dimension layer, not based on where your components, traces, or ground layers are. So again, they will gladly create a 100mm x 100mm board since that's what your dimension layer says ...
Your solution here is to first draw the dimension layer to match your circuit and how big you want it. Once you're done routing, then redraw the dimension to the actual size of the final board. Or, you can always hand route everything as opposed to using the autorouter.