secure site - page cannot be displayed

[petben]

what does it mean if random secure sites give the page cannot be displayed error, but if in IE10 'send page by email' shows the complete and rendered page in the email?

 

 

the sites are crashing in IE and Firefox, for some users and not others with identical settings. all v strange, any advice would be great! reset IE settings works for a bit, then crashes again! argh.