There was a known hack - well at least it acted like one - which would allow a user that was not logged on to access the export page template on older versions of dnn.
The url you are seeing is how that hack appeared
On most sites - including your own I would suggest attempting to access that url will force the request to automatically be redirected to the LOGIN page.
IF you check the url on your own site - (add your domain name to the front) - it will take you to your login page.
So in terms of the hack/bot hit - its not likely that you are being effected in any way ...
HOWEVER - it is also a possible precursor for the spambot attack - in that it is ONE of the possible ways that the spambot attack attempts to work out of a site is running DNN.
I would suggest that you looking at upgrading to the latest version of dnn that has solutions in place to deal with that issues as well.
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Finally the reason you are seeing an exception when this bot hits your system is a little more complex.
There have been a number of known issues in older versions of dnn - that cause exceptions to happen with a bot or spider or crawler hits a site for the first time - especially if the site is not running a keep alive system.
A lot of those exceptions can be traced back to a serious issue in the way the scheduler used to work - effectively if a crawler makes multiple requests at the same time (something the always pretty much do) the scheduler can be falsely made to launch multiple times - which eventually causes an exception .
The only solution that I am aware of which deals with that issue is an upgrade of dnn to 7.3.3.
Westa