This is probably a simple mistake somewhere, but when I try to add an external MapServer service (meaning created/hosted by some other site) to an ArcGIS.com map when I'm logged in to my Organizational account, it acts like it can't see the service. However, if I log out and create a map on ArcGIS.com without signing in, I can view the service no problem.
I'm the Administrator for my Organization, so surely it's not a permissions issue, right?
Add the item to your content by using the rest URL. Then search for it within the webmap.
Sometimes adding items directly into a webmap gives random errors without reason, but when pushing it into your content first it can eliminate this issue.
Hi James - thanks for the tip, but still no go. When I try to add to my content it says: "Service '' does not exist or is inaccessible."
This is the service I'm trying to add:
It adds just fine to an arcgis.com map when I'm not logged in to my organizational account
Is your organization configured to allow SSL only? If so, the service may be getting blocked by the browser when add item attempts to make info requests to get the service information. You can switch switch the service URL you're attempting to add to HTTPS (though it doesn't look like the server supports SSL in this case).
You should also be able to override the browser block - the behavior for each browser is different, but you might see something in the URL input box. Like a shield or something else that indicates a resource has been blocked. Clicking the shield will allow unsecured http resources to be added (be aware when doing this, it means the page is no longer fully secure. So this should only be done with trusted http resources). Here's Chrome for example:
Here's some info with links that go into more detail about each browser's mixed content support / behavior.
Aha, this might explain some things. Yes, we have it configured to allow SSL only right now. I see how to do what you're saying in Firefox, but when I click on the shield in Chrome, I'm not presented with the same option to allow unsecure content. Also, in IE I don't get the option at all.
Would it be completely irresponsible to disable SSL only?
Enabling / disabling SSL only is a question best answered by you / your organization. The documentation for configuring your organization's security settings has some more info: Configure security settings—Help | ArcGIS
And yes, unfortunately, each browser behaves differently..and can change when the browser automatically updates.