Error - Can not find the tag library descriptor for "/struts-tags"

This is probably Eclipse getting a bit 'confused' rather than a genuine error.

I had the same thing yesterday when working through a Struts 2 tutorial, but it disappeared after opening/closing the JSPs.

In ECLIPSE: Right click on the project and select the option "Validate". That's all.

Have you added the struts2-core-.jar to the libraries of the project? If you have try to clean the project.