I was trying to install FckHtmlEditor like copying files to Bin folder and Provider and changing web.config file. And now 3 portal that I had are giving me error: Description: An application error occurred on the server. The current custom error settings for this application prevent the details of the application error from being viewed remotely (for security reasons). It could, however, be viewed by browsers running on the local server machine. Details: To enable the details of this specific error message to be viewable on remote machines, please create a tag within a "web.config" configuration file located in the root directory of the current web application. This tag should then have its "mode" attribute set to "Off". <!-- Web.Config Configuration File --> Notes: The current error page you are seeing can be replaced by a custom error page by modifying the "defaultRedirect" attribute of the application's configuration tag to point to a custom error page URL. <!-- Web.Config Configuration File --> HELP! HOW TO MAKE UNDO ? OR WHAT CAN I DO ? I HAD ALMOST READY 3 PORTALS, WHAT TO DO FOR NOT TO REINSTALL DNN ? REINSTALLING I'LL LOSE MY PORTALS ! I had same error when I was installing skins made by me BUT I was just deleting skin from server and it was solved.

No, the one thing that you SHOULD NOT do is start to reinstall.

Next, tell us which version of DotNetNuke you are using.

Did you make any backups before you started?

If you did make backups, simply reinstall them.

If you didn't make any backups, make a complete backup of your web directory AND your database before doing anything.

Next, save a second backup of your existing web.config.

Now, add that tag or modify the existing one in your web.config so that you can see a more complete error message. Then show it to us.

We'll deal with fixing your problem after we know more about the editor. Most likely, though, there is a simple error in web.config that needs fixing.

Thanks god,I solved problem: I replaced Bin, Provider folders and we.config file from original Dnn insallation folder.
I lost insalled modules but it's nothing. I did make backup of web.config file and it didn't help. Dnn 4.5.

Thank you very much for answer and help.
Question: how can I make backup of complete Dnn installation ?

If you've replaced web.config with the original, make sure that you've copied machineKey. If you don't you won't be able to login.

I'm not sure how you could have lost modules, unless you removed code wehn you removed the other folders. I suppose if you totally replaced the bin file, you lost any dlls associated with installed modules. You should be able to reinstall the
modules.

To make a complete backup of your site:

1. Use SQL Server Management Studio (or Express) to make a backup of your DotNetNuke database. That's the database that the web.config specifies.

2. Using FTP or some other approach, make a copy of the entire web directory.

Thank you very much for your help. From now I never will make changes in Dnn installation without making backup.

Yes, repeat this mantra ... ALWAYS MAKE BACKUPS ... FIRST!