You can either download the beta-version from the bottom of this page or follow these instructions:
How to open newer versions of capx files
unzip the capx and edit the caproj file in a text editor
find where is says (for example)
<saved-with-version>21100</saved-with-version>
and replace with an older number eg
<saved-with-version>17000</saved-with-version>
save and try