iOffline requires Adobe AIR to run. Unfortunately, you might have  version 3.4  installed which has a bug that prevents iOffline from getting installed or updated.

While Adobe is fixing this bug, as a temporary workaround you can get iOffline to work by downgrading to Adobe AIR v3.3. This is an easy process:

Windows:

•     Go To > Control Panel > Programs and Feaures (in xp:  Add or Remove Programs)
•     Select "Adobe AIR" and uninstall the runtime.
•     The link http://helpx.adobe.com/air/kb/archived-air-sdk-version.html allows you to download and reinstall the previous (3.3) version of Adobe Air.

Mac:

•     http://helpx.adobe.com/air/kb/archived-air-sdk-version.html to uninstall the current version (Double-click the "Adobe AIR Uninstaller", which is located in the /Applications/Utilities folder)
•     reinstall the previous version of Adobe Air Runtime.