Guide refresh problem

Hello.  I have been having trouble with the signal not found 771 error and with the Guide not received 920 error for a while.  I believe that a neighbor's tree was the problem with the 771 error.  I found that moving a single limb seems to have taken care of that.  I'm still seeing the 920 error frequently.  I am occasionally unable to see a favorite regional sports HD channel after this has occurred.  I just get the Directv logo screen.   I've found that if I change my display settings to show the SD channels that this forces the Guide to refresh.  The HD sports channel then becomes available in the next few minutes. 

I have checked my signal strengths.  Are all 80's-90's with the exception of sat 119 which is all 0's.  Questions:
1) Do I use sat 119 in No. VA?  Would it have anything to do with my guide refresh problem?
2) Is this likely to be an alignment or obstruction (tree) problem if the refresh trick always works?

I haven't called customer service yet.  This has been intermittent and I've been hoping I can troubleshoot this myself without the hassle of a service call.  Any advice is greatly appreciated.  Thanks very much.