When I try to view a pdf in reader/acrobat X, TeXnicCenter hangs for about half a minute, before saying that the DDE command failed. I think the offending code is
dwOverallTime += 10;
*conv = DdeConnect(inst,serv,top,NULL);
while ((*conv == 0L) && (dwOverallTime < dwTimeOut));
in DdeCommand.cpp, which (I presume) gets run on the UI thread (with dwTimeOut == 10000).