SVN working copy upgrade failure

Question

In my VS solution I have project with old working copy format. When I try to upgrade it using AnkhSVN, I'm getting this error:

SharpSvn.SvnMalfunctionException: Subversion reported a malfunction 'parent_node || entry->schedule == svn_wc_schedule_normal' on line 1666 of '..\..\..\subversion\libsvn_wc\entries.c'.
   at ?A0xa69717b0.sharpsvn_malfunction_handler(Int32 can_return, SByte* file, Int32 line, SByte* expr)
   at svn_client_upgrade(SByte* , svn_client_ctx_t* , apr_pool_t* )
   at SharpSvn.SvnClient.Upgrade(String path, SvnUpgradeArgs args)
   at Ankh.Commands.UpgradeWorkingCopy.<>c__DisplayClass2.<OnExecute>b__0(Object sender, ProgressWorkerArgs a)
   at Ankh.ProgressRunnerService.ProgressRunner.Run(Object arg)

Have someone encountered this problem? Any solution?