I had this issue for dependencies that were created in other projects. Downloaded thirdparty dependencies showed up fine in the build path, but not a library that I had created.
SOLUTION: In the project that is not building correctly, right-click on the project and choose Properties, and then Maven. Uncheck the box labeled “Resolve dependencies from Workspace projects”, hit Apply, and then OK. Right-click again on your project and do a Maven->Update Snapshots (or Update Dependencies) and your errors should go away when your project rebuilds (automatically if you have auto-build enabled).