Please be sure that, after editing the 'global' file, and saving it, you stop and restart DP
REgarding the actual error, you can set SmMaIdleTimeout as high as you want, it is probably still going to timeout. We have found setting KeepAlive to 10 or 15 minutes is usually the best way to deal with this. Please view the attached document for a fuller explanation
I would recommend that you implement KeepAlive on any disk agent or media agent that is timing out, and I also feel comfortable in recommending that you enable KeepAlive proactively on all your servers, although, it is probably not necessary on your cell manager unless it is one of the systems timing out
On Windows systems, after editing the 'omnirc' file, you must stop and restart the DP INET service