OK, I think that is the problem. I want to release a new version (1.5.0) tomorrow (sunday). I try to integrate something into that version that hopefully helps with that problem. My mod will then basically skip traders it can't retrieve prices from.
File
Show Me The Money 1.5.0

M-m-m-m-monster update...
- Added a color coding feature. The names of the items are color coded now (by default, the familiar WoW color scheme from poor to legendary). The colors and thresholds can be configured.
- Ammunition is colored based on its penetration power rather than its sale value (can be turned on and off in the options). The thresholds are currently hard-coded (Poor < 15, Common < 25, Uncommon < 34, Rare < 43, Epic < 55, Legendary >= 55).
- Significantly improved support for the