Sorry to hear you're having trouble.
Would you please identify the specific version of both DMS, and PageLESS that you're using?
I have tested the current version of PageLESS (1.2.2) with the latest release of DMS (1.1.2) and have not been able to reproduce your error.
I agree that it sounds like this may be PageLESS related from what you've described, but I need some more information.
If the DMS Editor is stuck loading, that generally implies a PHP error or a JS error. JS errors are easy to find through the chrome dev tools console. PHP errors need to be searched for (as the loading modal is covering everything).
The documentation for troubleshooting common issues is a good place to start: http://docs.pageline...g/common-issues
Please provide any screenshots if possible of any errors you find.