It's possible you tried registering twice and the activation number you got was for the first registration.
Ok, after looking in the database, it seems your account somehow got in there twice. That's not supposed to happen.
Looks like one had a misspelled email address. Considering the low ID number though, that must have been registered while still early in the testing phase. Perhaps it has been fixed already. I'll have to run some tests. I deleted the first account, you should be able to activate the other one now.
Edit: Yeah, looks like that's been straightened out now.