Hi Clockworx,
Check to make sure you have allowed 3rd party cookies and pop ups in your browser settings. Those are needed for the in game pop up screens to show.
If you do not want to open up your browser to all 3rd party cookies or all pop ups you can add the following web sites to the exceptions for those settings:
Slashkey.com
L1.slashkey.com
Facebook.com
Apps.facebook.com
Trialpay.com
Also , if you have an ad-blocker plugin in your browser make sure the above web sites are also allowed in that too.
Be sure you close and restart your browser for those changes to take effect.
Please note to add the sites in exceptions:
In Chrome you have to go to Advanced settings at the bottom of the options page.
In Firefox add the sites under the Content tab for pop ups and under the Privacy tab for cookies. For the cookies to work you must set the History setting to "Use custom settings for history"
I don't have any information on where to set these in the other browsers as I don't use those. You may want to check your anti-virus and anti-malware programs for these sites to make sure those are not blocking them either.
The problem with this was the Facebook update done at the same time as the Flash update that has cause the problem with the lists.
I have done it all as set out above and still blank screen, even disabled all add blockers, no go. Seems as if train boosting as it was has come to and end for me.