We are aware about issues when trying to invite sub-accounts. This is how the scenario would generally play out:
1. The parent account (e.g account 'abc') would invite a sub-account following the instructions specified here:
2. The sub-account recipient would get an email similar to this one:
We're happy to inform you that your friend abc just invited you to create a sub-account for account 'abc'.
Please use the link below (which is valid only for 3 days) to create a sub-account: http://saucelabs.com/sub-accounts/invite/finish/xxxxxxxxxxx
3. When the sub-account click on the email link in order to become a sub-account he/she would get the following message:
You can't convert 'abc' to become a sub-account of 'abc'. These are the same accounts!
Now, the question is why is this happening?
This is happening because during the time that the person was trying to set-up his/her account by following the email link, he or she was already logged in to Sauce Labs using another account. I know that this might be a little bit confusing, but overall the rule is that there should not be any Sauce Labs accounts logged in on your end for the link to work.