I've been trying to play this online for the last few days and I've had nothing but headaches with the Stardock system.
I purchased the game using a gmail account. The order went through successfully and I got my serial number. I download impulse and log into it using my regular username and password. I activate the product and it goes through just fine.
Here's where the crazyness begins (and is speculation on my part, the real problem may be different)
The game was purchased using a gmail account, but my stardock login was created years ago with a now disfunct hotmail account. Because of this, the game does not recognize them as being the same account.
I found an obscure link that allows you to change the e-mail address of your account. I did this and updated my email to the correct gmail account. I re-activated the game on the account and it actually went through, but it still does not let me play online in the game. It still says the username or password is invalid.