Deirdre,
This is not an issue that we are aware of. We are currently at software version 1.7.58968. Try updating the software to the latest version by selecting Help/ Check for updates. You will also want to ensure that Java 6 and Adobe Flash 11 are up to date. (case# 235364)
Once the software is up to date if you are still having issues, there is a link below with some ActivTips that may help as well.
www.prometheanplanet.com/.../activtips
In the search box type in "Containers" and all the video/tutorials that have to do with containers will be displayed there.
Thanks!