Eclipse: XXX is not a valid line number in YYY

Press Ctrl+Shift+R and enter YYY.java. Eclipse will then tell you which YYY.java it can see. Chances are that it sees more or other source files than you expect.

If there is just a single file, make sure it's the correct version. Maybe Eclipse mixes a new bytecode JAR with an old source JAR.

The maven error message means that it's missing M2_REPO\org\apache\...\some-version-sources.jar This file must be in the same directory as some-version.jar for Eclipse to attach the sources to the binary JAR.

If you have the sources, copy it there. If you don't have them, there is a chance that Eclipse can download them for you. Open the context menu for the project -> Maven -> Download sources ... wait ...