Environemnt= Exchange 2007/2003 mixed 2007 enviornment has 3 CAS servers, one in each site and 1 CCR cluster in each site, all on sp3 update rollup 7. One AD forest with 3 submdomains site 1 internet facing CAS with external url set to https://webmail.company.com/ "Use forms-based authentication" enabled sites 2 and 3 CAS servers not internet facing, no External URL configured and "Integrated Windows authentication" enabled OWA works fine for users on sites 1 and 2 when using https://webmail.company.com or https://webmail.company.com/owa users on site 3 can only access owa using https://webmail.company.com/owa, if they enter webmail.company.com it fails with this error " 500 Internal server error, there is a problem with the resource you are looking for, and it cannot be displayed. ISAPI extensions setup on all mailbox servers. Any ideas Thanks in advance

The 500 error is just IIS's way of telling you that some server-side code failed to execute properly. You'll need to get something a bit more specific than that. Have a look in your IE options and make sure that the 'Friendly HTTP Errors' option is unchecked (the 'friendly' errors hide the most useful information), and then try again.Mobile OWA For Smartphone www.leederbyshire.com email a@t leederbyshire d.0.t c.0.m

hi, Please check the http redirect in your IIS on your problematic site cas servers. Also check it on your normal cas servers. Compare them, see if there are some different between them. I think may be you should set the simplfy owa URL. Please see this link:http://technet.microsoft.com/en-us/library/aa998359.aspx hope can help you thanks,CastinLu TechNet Community Support

hi, Please check the http redirect in your IIS on your problematic site cas servers. Also check it on your normal cas servers. Compare them, see if there are some different between them. I think may be you should set the simplfy owa URL. Please see this link:http://technet.microsoft.com/en-us/library/aa998359.aspx hope can help you thanks,CastinLu TechNet Community Support