Hmm, yes that definitely seems out of place - It looks like your version of XSE doesn't recognise the command for some reason. This may be because you're using an outdated version of XSE, but I'm not confident in saying that, seeing as how your msgbox command is working correctly.
Luckily, there should be a work around for this problem. The wildbattle command doesn't actually exist in the ROM, it is a combination of the commands 'setwildbattle' and 'dowildbattle' which was created for the convenience of hackers. You should be able to get your script to work if your replace your wildbattle line with:
setwildbattle 0x6 0x1E 0x8B
dowildbattle
And if that doesn't work for another unknown reason you can insert the entire thing in HEX. You will have to replace the wildbattle line with this:
#raw 0xB6 (setwildbattle)
#raw 0x6 (Pokemon Number)
#raw 0x1E (Level)
#raw 0x8B (Held Item)
#raw 0x0 (filler)
#raw 0x0 (filler)
#raw 0xB7 (dowildbattle)
I doubt it will come to that, but you never know :P
Edit: I was replying when you messaged me lol