Redmine

I installed new version of Redmine on my Ubuntu server a couple days ago. I properly configured Apache for correct working Subversion with Redmine. I created public project. But when I try to commit some files in this project without entering username (it is simply empty) in TortoiseSVN dialog on local machine I get the following error:

Error: Commit failed (details follow):
Error: Server sent unexpected return value (500 Internal Server Error) in response to
Error: MKACTIVITY request for '/svn/mmm/!svn/act/008182d9-97ee-2740-9a75-5c734c292d4c' ".

The following string in error.log of Apache:

Use of uninitialized value $salt in concatenation (.) or string at line 471 Redmine.pm.

This line from Redmine.pm is:

my $salted_password = Digest::SHA::sha1_hex($salt.$pass_digest);

If I uncheck "Public" to this project everything is ok. In this case TortoiseSVN let me authenticate repeatedly in SVN from one dialog window (if I enter empty or incorrect credentials)
What is the problem?