In case you're coming to the party late, and maybe try to read an older post of mine about this...
Apparently the rules have changed just a bit.
When you "Add a new blog" at BlogMailr, you're going to want to use the following credentials:
Web Address of your blog: http://geekswithblogs.net/<YOUR BLOG NAME>
In the past this was presented a bit differently, and apparently you need to generate a new one to make the magic work.
The jury is still out on if they've blocked posting to GWB from here, but I'm going to try a 'Cream post via BlogMailr next.
I'm also going to try two Tags on this one, so we'll see what happens.
If I can edit this, I'll say chaining the two tags together like this: [Tag:One][Tag:Two] worked great!