First, make sure you are running the 060426 build of Version 5.00. If not, (a) get the latest update from this website, and (b) register your software so your receive the e-mail announcements when new builds are released.

Second, read this post , which discusses the ISOGEN Export Interface in Version 5.00.

Third, just for information purposes, the icon on the toolbar button is a "lower case 'a'", which is the logo for Alias the developer/owner of ISOGEN.

Fourth, review the CAESAR II FAQ, which can be found here, on this website . Click on the "Isogen" link in the Contents to review the problems and solutions other users have experienced with this utility.

A few questions:
1) What is your Operating System and Service Pack?
2) What local language setting are you using?