No one likes to be the bearer of bad tidings but if you peruse the forum topics and the search box you'll find that you aren't alone when it comes to Blogger's failure to recognize your username and password when attempting export and import your blog.
Also when searching the net and doing a blog search you will find MANY Blogger subscribers who are experiencing the very same username and password recognition difficulties even though they are not attempting export or import of their blogs. In fact there seems to be a very unhappy Blogger community out there when it comes to this sign-in failure problem, the downtime problem, and the lack of support problem dating back to about two weks ago now.
Although I could be wrong, I'm speculating that this problem export/import problem seems to be at Blogger's end of things.
Volunteers on the wordpress.com forum do not have backend access and are unable to help you with either of these problems. I think the best approach to take is to send in a feedback with a link pointing back to this thread and then to be very patient, as there are many similar requests in line ahead of your own.
I'm sorry I couldn't be the bearer of better news but rest assured that our beloved sysadmin geeks here at wordpress.com are working their butts off trying to address these problems.