Hi Kurgbe,
This is not a known issue. Before doing anything else please make sure that you are using the latest version of the program, which is 5.1 Build 730 (check this with Help > About). If you need to update get the latest installer here and install on top of your current version:
http://www.ec-software.com/downloads.html
If this doesn't help the next thing to do is to check whether it is just this one project or all projects. Open another project or create a new project to check this. If it is really just this one project then we need to have a look at it. Save the project in single-file HMXZ format, pack it in a ZIP or RAR archive and mail it to
support AT ec-software.com (replace the AT with @) and we'll check it for you. Please include your full name in the mail so that we can identify your user account.