Which version of DSLstats is this?
Notwithstanding the answer to that question, it's not a necessary part of the configuration to make a selection from that dropdown - it's only used as a shortcut to filling in the login details, which you can do manually anyway.
Is this a new issue which you haven't seen before, in which case, what has changed?
[Later] It's occurred to me that a likely reason for that dropdown failing to work would be the absence of the file routers.dat from the main DSLstats directory. It's part of the downloaded archive, so if it's got lost somehow you should be able to retrieve it by downloading DSLstats again.