Try a vise grip.  It has worked for me MANY times in the past.
Clean the bolt head first and make sure you apply A LOT of
pressure.  Turn it very slowly while someone is applies the
brakes to keep axle from spinning.

In the future, you might want to clean the crud out of the bolt
heads and give the allen or star socket a tap with a hammer to
make sure its seated properly.  Always apply pressure very
evenly.  This  has worked for me very well to keep bolts from
stripping.

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Chris S.'85 Westy Camel -> http://www.knology.net/~vw/vws/camel/ '84 Westy Hershey -> http://www.knology.net/~vwghost/hershey/ '01 NB TDI -> http://www.knology.net/~vw/Beetle.jpg