Why are you using a Post-Text-Item trigger instead of a When-Validate-Item trigger? How is your user leaving the field that this trigger is attached to? If the user is mouse-clicking to leave the field - the Post-Text-Item trigger will not fire. Take a look at the "Post-Text-Item trigger Restrictions" listed in the Forms Help system for this and other restrictions on using the Post-Text-Item trigger.
Thank you for that insight. Alert is working fine!