Cannot change version of project facet Dynamic Web Module to 3.0

เมื่อสร้าง web project defalut ใน eclipse จะได้ servlet 2.3
ถ้าเราแก้ web.xml เอง


จะทำให้ เกิด
Cannot change version of project facet Dynamic Web Module to 3.0.
วิธีแก้ไขคือ
1. คลิ๊กขวาที่ eclipse project เลือก properties -> Project facets -> เอาติ๊กถูกที่ Dynamic Web Module ออกกด apply

2. คลิ๊กขวาที่ eclipse project เลือก maven -> Update Project

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IWAE0053E An internal error has occurred running validation on project. The deployment descriptor

Method 1

As suggested by another developerWorks page, I was able to fix it by:

1) Close the project (Right-click the project, Close Project)
2) Open the project (Right-click, Open Project)
3) Force a full rebuild

And, no, skipping straight to #3 didn’t fix the problem for me. But, these three steps did.

Method 2[Haven't tried this methos
This snippit that was posted to the IBM developer works forum :

I had the same problem, and resolved it by opening the .settings folder of the EAR project and editing the org.eclipse.wst.common.component file. The war module listed in the error message is missing as a dependent module, so I added it:
http://www.blogger.com/img/blank.gif

WebModule_
uses


where
is the generated WebModule value from META-INF/.modulemaps file for the war
is the name of the war project in the workspace


ref : link