Redirect to LogIn form

I have some strange problem with the blog. When I access some of the plugins, if I change something, and hit «save», WordPress redirect me to the login form of my blog. Login does not work, because I have already authorized. So I just can not enable some plugins for the blog.

This happens when I install a plugin or theme through the «One Click Plugin Updater», when I try to designate a page redirect after «Peter’s Login Redirect» in a number of other plugins.

I have installed engine to another address, on the same topic, and all the same, I have been using for experiments on the topic, and there is no such problems. I mean, it seems a specific bug specific installation.

I tried to disable all plug-ins, leaving only one – login redirection, so it set the redirection. And still the same everything, throws in the authorization form.

What can i do?