I seem to be having the same issue.
My app was working with 7.0, but Digi began shipping new modules (distinguishable by having a T under the barcode) and when you load a 7.0 app into one of these, it doesn't work. Digi said I needed to upgrade to 7.3, so I did. That seemed to work, but apparently it will work for a while, then fails again. I power up, yellow and green both on, after a bit, yellow goes off for a sec, then comes back on, and from then on, both lights on solid. A working unit will have the green turn off when the yellow comes back on, then flash as it begins communicating.
Since this was done on straight 7.3, I've since loaded all the patches, and rebuilt my image.
Trying to recover these modules, I got Tftpd32 running, and it acts like it is pulling in the fresh image, but nothing changes.
I suppose I could try the 7.4 that just came out, but it was a PITA just having to update to 7.3 a few weeks ago.