Complex sentence: The username you've picked appears to represent a group, organization or website, so I blocked this username per our username policy, but don't let that discourage you: please take a moment to with a username that represents only yourself as an individual.
Split into simpler sentences: The username you've picked appears to represent a group, organization or website, so I blocked this username per our username policy. Please take a moment to with a username that represents only yourself as an individual.