to prevent not being able to backing up after hitting a forbidden page you
must edit the pxyerr.htm file with this:

change from this line
setTimeout( "window.location.href = sTargetURL", 0/*delay in
milliseconds*/ );

to this line

setTimeout( "window.location.replace(sTargetURL)", 0/*delay in
milliseconds*/ );

You only have to do this if you make your own error pages, if you are using
the standard bordermanager files you don't have to do anything.....