That makes two of us .....
I too thought that if every other transponder was zero's it was an LNB as well.
To get even transponders the receiver generates an 18v signal. To get odd transponders the receiver generates 13v. If there's a poor connector (loose, corroded etc) this can drop either the 18v or the 13v below the detection threshold and so you lose either even or odd transponders. This is by far the most common cause of loss of even or odd transponders.
If you have a multiswitch the effect can be even more specific. For example, there are four cables from the dish to the WB68 multiswitch. One carries 99/101 evens, one carries 99/01 odds, one carries 103/110/119 evens and one carries 103/110/119 odds. So from the pattern of the missing transponders, you can often determine exactly which cable/connector is faulty.
A situation where you have a multiswitch and you are losing odds or evens on ALL the satellites indicates either a faulty multiswitch or LNB, or a situation affecting all the cables (cable run too long or trying to use RG59, or using RG6 CCS on very long runs - all of which can cause voltage drop)