When I try to look at my Profile Graph for my meter account for Mug and Bean, it says there is no Data Available. Why not? Please fix this!

What does your problem meter list say?

I don't know about a Problem Meter list. When I select my meter, if gives the overview screen, and there is a yellow line around the box.

To see your Problem Meter List, select Tools, and it will open up a sub-menu. It should be near the top: on your account it is the third line from the top. Click on it. Find your meter in the list, and see what it says under the Problem column.

It says it Could not connect. Is this a modem problem?

Yes.
Additionally, if you hover with your mouse over the Problem description, it will give you a technical error message. In your case it says: 'chechOut failed: 89270000000726492649 not in connectionPoolLookup'.
You are using an APN-less TC65 modem, which means the modem connects to the server over GPRS using TCP/IP, and the server then identifies it according to the SIM card number. What the message means is that this modem has not connected to the server.
To see a historical log of errors on this meter, select the meter on the left. Then, from the overview screen with the meter selected, click on View->Meter Read Logs. What do you see?

There is a log for all the read in attempts today, with columns for the meter number, time, method, outcome, and so on.

According to this read log, we've tried reading it many times today, and at no point in time has the modem been connected to the server.

We've bought this assembly from you. Why isn't it working?

If you select Edit->Meter Details, you can see that it has been installed on 14 April 2011, and it has called in fine until 29 July 2011.
Something went wrong on 29 July.
This could be a SIM card problem, or a signal problem, or the power could be off.

Do I have to go out to site? Is something wrong at site?

You can possibly try putting airtime on the SIM if it is prepaid. Or you can SMS it if it is a KOCOS and see if it replies. Now in your case it is not, it is a TC65. So if you have the relevant utility program, you can try calling it over CSD (the support office in Kempton Park can usually help you with this). Or if you can get out to site, try putting the SIM into an old cell phone and browse the internet. If that doesn't work, it is the SIM card that is the problem.
Once you're on site, the problem might be obvious: perhaps units are off or disconnected, or the arial might be cut off, or some of the equipment might have been stolen.
This is not a loose cable problem, since the link that is broken is between the modem and the server. The modem itself does not have power or signal. The modem itself could also be faulty: check that the LED lights are on, and that one of them double flickers (that indicates GPRS signal).