To show error details like the stack trace, edit the web.config of your web application:

1. Change <SafeMode CallStack="false" to <SafeMode CallStack="true"
2. Change <customErrors mode="On" to <customErrors mode="Off"

Now you will see your full exceptions, no more "unexpected" or "undefined" SharePoint 2007 errors.

1. Enable anonymous access for a web application from the Central Admin.
   - Central Administration Home Page > Application Management > Authentication Providers
   - Select the web application where you want to enable anonymous access
   - Click the "default" Zone
   - Mark the checkbox "Enable anonymous access"
   You don't have to do anything on the IIS Manager. Enabling it from the Central Admin page will also enable it on IIS and modify your web.config.
   
   
2. Explicitly turn it on for the sites you want to be accessed anonymously.
   Browse to your site, click Site Settings > Advanced Permissions > Settings >Anonymous Access and turn on anonymous access for the site.
   
   
3. For further settings search your Sharepoint help for "enable anonymous access".

If you get this error by browsing video files with Windows Vista, you've  probably installed Nero Burning Rom.
To fix this problem, rename or delete the file "NeVideo.ax", located in "c:\program files\common files\ahead\dsfilter\".

Other possible solution:

http://www.jcxp.net/forums/index.php?showtopic=12152&st=20
Download Directshow filter manager, extract the exe to somehwhere. Open explorer, right click on the extracted exe and select run as administrator, allow the app to run.

Next, click the module column header (so click on module), this will sort the list by directory name (as you would to select a column in excel), scroll down and find the reference to the nero dsfilter folder and nevideo.ax - for example on my pc I looked for c:\program files\common files\ahead\dsfilter\nevideo.ax, I found 2 entries, u may have more or less. Double click each entry and change the filter merit to 00200000 then click set new merit. Close the window and repeat for each entry.

1. Navigate to ~Program Files~\Common Files\Microsoft Shared\web server extensions\12\bin.
2. Execute stsadm -o spsearch -action stop
3. Delete your existing search database, e.g. WSS_Search_"your server"
4. Recreate your search database, be carefull to use Latin1_General_CI_AS_KS_WS as collation and your domain account for search service as owner of the DB.
5. Execute stsadm -o spsearch -action start

=> your MOSS 2007 search database will be recreated.