During my last project I was involved, I used Eclipse IAM plugin for integration with Maven. It caused many problems, mainly Class not found exceptions and issues with Tomcat server.
Generally I perceived that Eclipse IAM tends to lose jars from pom.xml, what leads to unexpected, bizarre time wasting NoClassDefFoundError.
Unfortunately I hadn’t been sucessful in finding causes of my problems but I’d like to share with you my standard ‘IAM problems checklist’ 
If you have any problems try this (in specified order) :
- Use refresh, then fetch source jars option from maven menu.
- Try cleaning maven libraries, then do ’1.’
- After doing ’2.’, remove your app from Tomcat, clean server, then deploy again.
- Try removing whole server, then add it again.
- REMOVE AND REGENERATE WHOLE WORKSPACE
Any step mentioned above is not a joke. I had really to ‘reset’ workspace a few times to make things work again.. First three steps helped me in 80% cases.
I hope my tips will save your time.
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