Why won't iWork open after first installation

I have resently installed iWork '09 and the softwarre will not open. A notification comes up say the following:

Check with the developer to make sure Keynote, Pages, and Numbers work with this version of Mac OS X. You may need to reinstall the application. Be sure to install any avaliable updates for the application and Mac OS X.

I made sure that it was compadable with the version I currently have and have installed it several times. Any help would be great. Thanks!