In case you have ajaxified your map control, the ajax manager creates an UpdatePanel control and wraps your map control in this UpdatePanel. The UpdatePanel renders a DIV element by default and in case you are using height=100% for your map control, you should specify a height style for this DIV element as well. The easiest was to check whether this causes the problem with the height of the map control, is to remove the ajax manager and all other parent HTML elements of the map control so that it becomes a direct child of the splitter pane. You can use Firebug for FF or Developer Tools for IE to check this.
Regarding your problem with the map control disappearing when you have ajaxified your controls - I would recommend that you remove the RadAjaxManager control and test your page with UpdatePanel controls (with UpdateMode=Conditional) instead. In case the map appears and functions as expected, you should not have problems using the RadAjaxManager control.
In case you need additional help with that, it would be best if you open a new support ticket and send us a running test project that we can use to debug the problems.
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