Redmine

Could you tell us more about your environment, do you have plugins installed? Possibly also post the output of ruby script/about RAILS_ENV=production (in your redmine directory)?

Of course, I can.
Here are the infos:

About your application's environment
Ruby version 1.8.7 (i486-linux)
RubyGems version 1.2.0
Rack version 1.0
Rails version 2.3.5
Active Record version 2.3.5
Active Resource version 2.3.5
Action Mailer version 2.3.5
Active Support version 2.3.5
Edge Rails revision unknown
Application root /home/redmine/redmine
Environment production
Database adapter mysql
Database schema version 20100221100219

About your Redmine plugins
Timesheet Plugin 0.6.0
Customer plugin 0.2.0

First thing I notice is that you need Rack 1.0.1 for redmine 0.9.x, other than that, try disabling your plugins and see if the problem persists, if not enable them one by one again to find the culprit. (You can disable a plugin by changing its permissions so that the user running redmine can't access it.)

Thanks for the quick answer. I´ll try it out right away tomorrow moring.

I´ve tried to disable the two plugins, but no change.
When I try to update rake with: gem install rack -v=1.0.1 the system says Successfully installed rack-1.0.1 1 gem installed

After that my result of ruby script/about RAILS_ENV=production is the same as before.

In the gem list are two Versions of rack:

• LOCAL GEMS ***

activesupport (2.3.5)
builder (2.1.2)
camping (1.5.180)
cgi_multipart_eof_fix (2.5.0)
daemons (1.0.10)
eventmachine (0.12.10)
fastthread (1.0.7)
fcgi (0.8.8)
gem_plugin (0.2.3)
markaby (0.5)
memcache-client (1.7.7)
metaid (1.0)
mongrel (1.1.5)
rack (1.1.0, 1.0.1)
rake (0.8.7)
ruby-openid (2.0.0)
test-spec (0.10.0)
thin (1.2.5)

Now I have no idea how to upgrade the rack for my redmine.

Do you use the packaged version of redmine? In this case rails and rack are packaged with it, but it's still odd that you have rack 1.0 if it's the packaged version.

Anyway, I'd say you should file a bug mentioning the error trace you have in the original post as well as the output of script/about, please also add a link back to this thread so the others can see what we have already tried and discussed.

Finally, I want to tell you the result of my problem. After installing a new Redmine and copying step by step the DBs I found the table that causes the problem. After droping the content of the table 'members', Redmine workes fine.