There's a free trial version of a program out there called SMScool by AIM Productions that allows you to "Manage and send Smartphone SMS messages from your desktop PC!"
It transfers your messages from your phone to your PC and allows you to decide which to save on the phone and which to delete while keeping copies of all on the PC if you want etc. In addition you can write messages on your PC and send them via your phone.
For your problem, maybe it can retrieve your inbox hopefully containing the invisible messages off your phone and allow you to read them on your PC? The trial version adds a tag to the bottom of any outgoing messages you send, but other than that, I think it's fully functional.
Their official site is here
, but it's being worked on so you can't get the program there today.
You can get the trial AND the full program at Smartphone.net
Might be worth a try. Good luck!
edited to ad: there is a PPC version "Pocket PC, v1.12"
Devices: T-Mobile MDA (Cingular SIM), i-mate SP5m (sitting in a drawer at the moment while I attempt to migrate to PPC permanently), Cingular 3125 (unlocked and in use on T-Mobile), Motorola MPx220 (retired), Motorola MPx200 (retired)
Accessories: Plantronics Explorer 330 & 2G Patriot Micro-SD (use w/MDA), Kingston 2G mini-SD used in SP5m, Plantronics Discovery 640 & 2G San Disk micro-SD (use w/3125), Jabra A210 BT adapter + Motorola HS805 (retired)