What type of application are you trying to debug (a web app / desktop / windows service)?
We have come across this problem on web applications where the multi-threaded version of the garbage collector (serverGC) can cause problems and reverting to the standard workstation garbage collector can often fix this. Please see http://support.microsoft.com/kb/911716
for the instructions on how to change the garbage collector while running the profiling.
As most of the ASP.NET settings can be set in lots of different ".config" files you may also need to check and set the serverGC tag in the "global" web.config in the CONFIG folder of the .NET installation, in Machine.config and the local web.config.
There definitely should be an update available, as the latest version of ANTS Memory Profiler is 18.104.22.168. Quite why it should not find any updates I am not sure, and I apologise for that.
To manually update the program you can download and install the trial edition from our website, this will update your edition to the latest version.