Is it that I can not upload any demonstrations created with Mathematica 10?

You need to use version 9 to create the demo with, then you can upload it ok. See http://community.wolfram.com/groups/-/m/t/288532 for discussion on CDF support and version 10.

You can also try this workaround (and keep on using v.10)

The best solution I found (posted here) is:

• In MMA 10 export the notebook as CDF (File - CDF Export). Let's say you call it test.cdf and save it in D:\
• Close the CDF File and, always In MMA 10, open a new notebook (or use an existing one) and paste the code:

cdf = Import["D:\\test.cdf"];
Delete[cdf, Most@Flatten@Position[cdf, UndoTrackedVariables]];
Export["D:\\test_v9.cdf", %]

• After that you should have a new CDF file (named test_9.cdf and created in D:), compatible with the CDF Player v.9, that shouldn't give anymore any error message.

As for the next release of an updated version of CDF Player, it should be imminent at least according to the last post (by Andre Kuzniarek of Wolfram Research) published in this thread.

No, don't remove the UntrackedVariables.

As far as I can guess there can be other minor compatibility issues between file generated with MMA 10 and the previous versions of CDF Player (apart from the reknown UndoTrackedVariables). Another issue could be the graphics options since the color schemes changed heavily from v.9 to v.10. So you could try removing the non standard displaying options.

You could also ask the people who see the "pink" screen what version of CDF Player have installed (maybe they are on a way older version) and if, hovering on the pink image with the mouse, they see some tooltip describing the error.

Luca

Consider also that, according to the last post (by Andre Kuzniarek of Wolfram Research) in this thread, the release of a new version of CDF Player (compatible with Mathematica 10) is expected in few weeks.

Anyway, people having older versions of the free CDF Player, will need to update to the future new version to see the CDF file created with MMA 10 without errors (pink screen).