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This can happen if one uses e.g. TagExtraInfo in his/her project and project is not built yet. For exact steps to reproduce see issue #120395. Unfortunately, currently there's no easy way to fix this issue (ClassLoader created for JSP parser would have to look not only for compiled classes but also into the IDE cache probably for non-cimpled yet classes).
It's more enhancement IMHO, TM set to future.
This old bug may not be relevant anymore. If you can still reproduce it in 8.2 development builds please reopen this issue. Thanks for your cooperation, NetBeans IDE 8.2 Release Boss