I had the recent "Can'r reach master server" issue too. Rarely could see a server list at all, for a few days. Additionaly, when I took a look into the Red Orchestra log file, I found something like half a milion of :
<code>Error: UT2k4Browser_ServersList Package.UT2k4Browser_ServersList (Function GUI2K4.UT2k4Browser_ServersList.MyOnDrawItem:03B2) Accessed array 'Servers' out of bounds (490/468)</code>
errors, caused by just few minutes of browsing trough server lists.
Today I noticed the patch is downloading, and after game was patched I tried again - the server lists were refreshing normally now, but still the same hundred of thousands of errors. Only after I restarted the Steam, the errors don't log anymore.
Issue seem to be fixed for me... (after patch and Steam restart).