This article describes why you can get "Error response Error code 500. Message: Internal Server Error" when accessing any secure (https) site.

This error can happen when you use web acceleration software such as AT&T Worldnet Accelerator. While non-secure websites work with this software, secure websites do not. To solve the problem, you should configure Firefox to not use the web accelerator for https.

1. At the top of the Firefox window, click on the Firefox button (Tools menu in Windows XP) and then click OptionsOn the menu bar, click on the Firefox menu and select Preferences...At the top of the Firefox window, click on the Edit menu and select PreferencesAt the top of the Firefox window, click on the Tools menu and select Options...On the menu bar, click on the Firefox menu and select Preferences...At the top of the Firefox window, click on the Edit menu and select Preferences...
2. Select the Advanced settings panel.
3. Click the Network tab.
4. Click Settings....
5. If Manual proxy configuration is selected, continue to the next step. If not, these instructions won't solve your problem.
6. Deselect Use this proxy server for all protocols.

• • If it's not selected, leave it as is.

1. Delete any text in the text box beside SSL Proxy:.
2. To the right of SSL Proxy:, set the Port: to 0.
3. Press OK.
4. Click OK to close the Options windowClick Close to close the Preferences windowClose the Preferences window .