So you're running into an issue validating the service account entered? I'm assuming that you've double, triple, etc checked that it is correct. You can always opt to enter those credentials later. This will involve setting the account under Windows > Services.
On the majority of cases where I've seen issues here, the root cause is due to group or security policies in place in the environment. Upon initial installation you can use the work-around listed above. Now you may run into further issues when you want to upgrade. Moving from 2.0.x > 2.0.y does not require a re-validation of the credentials, but I've seen it required when moving from 2.0.x > 2.1.1.
If this is a temporary setup or an environment where you do not plan on doing a lot of customization in, then the work-around is sufficient. If it is an environment where uninstalling isn't an option, then I would suggest working with your network / security folks to pin down the group policy / security setting that's at play in your environment.
