That's either a 501 or 505 error.
Do you have friendly HTTP error messages enabled? Disable it in IE advanced options.
Do you have HTTP 1.1 enabled? Disable it in IE advanced options.
You may also wish to start IE with no add-ons. Either click a shortcut on the start menu or enter about:NoAdd-ons in the address bar. Then try the failing bookmarks.
From Microsoft.The website is unable to display the webpage (HTTP 501 or 505)
Error 501 (HTTP 501 - Not Implemented) means that the website you're visiting is not set up to display the content your browser is requesting.
Error 505 (HTTP 505 - Version Not Supported) means the website does not support the version of the HTTP protocol your browser uses (HTTP/1.1 being the most common) to request the webpage.
These errors might occur if you have HTTP 1.1 enabled. To disable HTTP 1.1, click the Tools button, click Internet Options, and then click the Advanced tab. Under Settings, scroll down to the HTTP 1.1 settings section, and then clear the check boxes for Use HTTP 1.1. These errors might also occur if a third-party product is interfering with Internet Explorer. Try closing all programs and then attempt to access the webpage again.