I'm tearing my hair out trying to get the styles customizer to work. When I click on Customizer I get the following error message on the right hand side window "
Unable to retrieve (SyntaxError: Unexpected token <)"

Thanks in advance.

Please check out this tutorial:
[Troubleshooting]

Warp 7 Customizer: "The current theme is not customizable.", "Retrieving Styles Data Failed", "Unable to retrieve" & related errors

yootheme.com/support/question/75099

Did you customized a file of the theme?
If yes, is that file still writable after you modified it ( does it have permissions of 644 ? )
Does that file not have illegal characters ?

Last option
Uninstall and then reinstall the theme, there is no indications that there is no illegal character issue.
Then do not copy and paste, but carefully type in your changes and test.