NetBeans, SVN, E155021, Problem and Resolution
The error message "E155021: Unsupported working copy format" indicates a version mismatch between the working copy and the svn client version. A repository checked-out with one client might be inaccessible to another SVN client tool.
NetBeans uses SVNKit as the default choice. However, the underlying SVN client in NetBeans can be configured in the Preferences / Options Dialog. E.g. if NetBeans complains, but the command line SVN client works, switch to CLI.
See you at Java EE Workshops at Munich Airport, Terminal 2 or Virtual Dedicated Workshops / consulting