It would be interesting to map that sequence out into the Sat's and polarities of each of those stations.
Going from memory, it sounds like you lock in a station on tuner 1 to something on the 101 sat.
Then, using tuner 2, you force the unit to switch to another LNB for one of the other sats, then switch to a source on 119 (HBOHD is there) and get your errors.
This is symptomatic of issues with multiswitches that are not getting enough power to switch.
Read this little blurb about the types of multiswitches available and remember that there is already one type A multiswitch in the AT9 dish. Couple that with another Type A, the Zimwell 6x8, and you have
TWO unpowered multiswitches plus any losses from cable runs, etc. to deal with.
[A] Non-Powered mechanical multi-switch - Cheapest in price. Has mechanical switching mechanism that is controlled by the power coming off of the DirectTV receiver. The DirectTV receiver changes voltages on the line depending on which transponder group it wants to look at. This multiswitch uses that voltage to move the switch.
(B) Powered mechanical multi-switch* - Mid range in price. Has a mechanical switching mechanism. It uses the voltage changes from the DTV receiver to determine what it should look at, but uses it's own external power to control the switch. Example of these are Channel Master and Terk multiswitches.
[C] Powered solid state multi-switch* - Most expensive. Completely solid state-no moving parts. Reads the voltage changes from the DirectTV receiver and electronically routes the signal to the correct LNB. Examples of these are Spauns, Trunkline, JVI.
*There are variations of and [C] which include signal amplification.
I had many of the same symptoms the OP lists, however, they totally went away when I added a class C multiswitch to the mix. Never seen a 771 in the last two weeks. Using the sequence above, could not reproduce the problem either after a few tries.
Like I say in a thread I started about ensuring one has correct power to the dish, many of our issues might be related to an overtaxed and overcomplicated switching scenario. The sequence listed seems to indicate that.