Please read the following text very attentively to avoid possible problems when you'll be trying to monitor several markets in MarketFeeder Pro. There are a couple of points that you should be aware of:

In order to prevent the software freezing while it is obtaining the data from the Internet or putting them into the Excel spreadsheet, such slow processes are maintained in so-called "threads". A thread is a separate process that is launched independently (in terms of time) from the main program. The more slow processes are required the more threads need to be created.
Every market you add to MarketFeeder Pro involves several threads - the slowest ones perform retrieving the list of selections and getting the current prices from BetFair. Plus sending these data into the spreadsheet.
Apart from refreshing the markets the software needs to keep an eye on the current list of your bets, your available funds, account statement and the list of triggers, offsets and books. It needs to write down the information about the markets into the log files. The price that we pay for the versatility of the software is the load on our computer resources.
Finally we get to the most important part: your computer resources are finite. You can't consume them boundlessly. There is a limit of total processes that can be run by your CPU, or bits of information stored in your computer's RAM. So it's not a surprise that MarketFeeder Pro operates within these limits. It's got the same CPU, RAM and Internet line that are shared by the other pieces of software and hidden system processes.
When you add too many markets to MF Pro and begin refreshing them too frequently the software does its best to provide the requested data at a given speed. Thus it opens as many threads as it can to make you be able to manipulate the main window and spreadsheet without the need to wait until the required data are obtained from BetFair. At some critical point - if you keep adding the load - the application will reach its allowed limit. This limit is different for every computer and depends on many factors. At this point the software will stop working and quit - because this is the way the operational system protects itself from crashing altogether.

Now most of you think that they are free to set the refresh rate to 2 sec and then load the whole today's race card into MF Pro. This is wrong. Try to do the same thing with Internet Explorer. Open 40-45 instances of your Internet browser, load a market into each of them and start clicking "Refresh" or "F5" every 2 sec in every window. You will soon notice that your computer needs a reset. So why do you think there's much difference with MarketFeeder Pro?

What I'm driving at is: consider your computer's capacity before you start loading it. You may have enough memory space and powerful CPU, but a bad Internet line which will hamper the refreshing. Or you may be running other resource-consuming software on the background (like Norton Antivirus or other kinds of firewall or anti-virus software). Applications like MSN, ICQ or chat windows also eat their share of Internet and CPU. Background Windows security update is the thing you need to take into account to.

So try to increase the load step by step - starting from maybe 3-4 markets and then adding more of them once you have realized that MF Pro is performing well enough.

And of course, don't forget to consider one or more of the following advices:

How to optimize the load on computer resources