The same happened to me just now (version 2.3-dev x86_64 March 18 2010 Linux).
This is what I did immediately before it happened:
* I swapped a healthy soldier for an injured one. It might be relevant to the issue as this soldier obviously dropped his inventory at the time I removed him from the aircraft.
* I meant to give the newly assigned soldier his equipment
* I realised that I needed one more machine gun
* I went straight to the "Buy/Sell Equipment" screen
* I bought a single machine gun
* Trying to go back, the game crashed as I hit the "Aircraft" button
Unfortunately, reproducing failed. Most likely because my most recent save was some time ago. As far as I remember, this is what had happened after my last save:
* I tried to intercept a UFO, and my fighter got shot down
* I built one more large and one more small hangar
* I bought a new fighter (Stiletto)
* now or probably a bit earlier the UFO (a fighter) was delivered to my UFO yard (I had completed a mission on a crash site prior)
* I saw a new UFO in approach and remembered that I didn't equip the new fighter yet
* I equipped it with my three remaining weapons (SHIVA (front), Sparrowhawk (left wing), TR-20 (right wing))
* I shot down the UFO
* now I went on with the actions I described above which led to the crash
This is what my console showed. Prior to this there are more [STATS] changes. I assume any earlier message won't be relevant. I attached the complete log in case it should be.
[STATS] 2010/03/19 12:02:39 - Soldier Yves Vasquez earned 46 experience points in skill #0 (total experience: 92). It is now 0 higher.Shutdown server: Mission end
==== ShutdownGame ====
music change to van_geoscape (from AlexFightmare)
Calling subsystems
...subsystem 'base' - saved
...subsystem 'research' - saved
...subsystem 'campaign' - saved
...subsystem 'hospital' - saved
...subsystem 'market' - saved
...subsystem 'employee' - saved
...subsystem 'aliencont' - saved
...subsystem 'aircraft' - saved
...subsystem 'installation' - saved
...subsystem 'ufostores' - saved
...subsystem 'production' - saved
...subsystem 'messagesystem' - saved
...subsystem 'stats' - saved
...subsystem 'nations' - saved
...subsystem 'transfer' - saved
...subsystem 'alien base' - saved
...subsystem 'xvirate' - saved
...subsystem 'messageoptions' - saved
XML Written to buffer (568596 Bytes)
music change to van_geoscape (from ufo2)
/usr/games/bin/ufo(Sys_Backtrace+0x15)[0x54a0b1]
/usr/games/bin/ufo(Sys_Error+0x73)[0x54a730]
/usr/games/bin/ufo[0x549e21]
/usr/games/bin/ufo(MN_ContainerNodeUpdateEquipment+0x103)[0x4d21a5]
/usr/games/bin/ufo[0x47c3c0]
/usr/games/bin/ufo(Cbuf_Execute+0x212)[0x4e9631]
/usr/games/bin/ufo[0x43604b]
/usr/games/bin/ufo[0x4f2717]
/usr/games/bin/ufo(Qcommon_Frame+0xc3)[0x4f21c4]
/usr/games/bin/ufo(main+0x45)[0x549e69]
/lib/libc.so.6(__libc_start_main+0xf4)[0x7effa7719a44]
/usr/games/bin/ufo[0x428c69]
Error: INVSH_AddInvList: No free inventory space!