Get the html source from that screen shot where half the window is greyed out. There was an engineering special for 4.0(3) that addressed this type of behavior. I don't recall what the ES number was, but only ES68 is available for download from CCO. You'll need to open a TAC SR to get that ES.
The source of that html should have some lines in it that will indicate a global.asa problem if this is the same problem I'm thinking of.
I just got through working a case with this very issue. Except my problem was not limited to after deleting a subscriber. If we saved any change at all to an existing subscriber and then tried to add a new subscriber the page would timeout. We were also running 4.04. The resolution was to install SR1 and then ES_95. Email me if you need any help.
These are the paths to get to each CCX logs through CLI. They may be helpful if you are having issues accessing RTMT or downloading logs through it.
If you want to download them you have to prefix "file get " and you can add one of the options (re...