Could be lots of things. Post your .asc file and I'll have a look. It seems that FROM and TO are not how you specify a range over the abscissa. This from the LTspice Help file:
The range over the abscissa is specified with the points defined by "TRIG" and "TARG". The TRIG point defaults to the start of the simulation if omitted. Similarly, the TARG point defaults to the end of simulation data. If all three of the TRIG, TARG, and the previous WHEN points are omitted, then the .MEAS statement operates over the entire range of data. The types of measurement operations that can be done over an interval are: AVG, MAX, MIN, PP, RMS, and INTEG.
ETA: It seems from the .meas dialog box that the FROM TO specification should be allowed. So I'll need to dig a bit deeper. I'll await the posting of your .asc file.
In the schematic:
Alt-Click the item of interest. A "power" trace appears in the graph
Then, in the graph:
Ctl-Click the new "power" trace. A popup displays the average over the length of simulation