Yeah, you shouldn't be experiencing any problems with those specs. Few things I can think of:
a) the disk you're loading from, is it okay? If you're loading images from another floppy, is it a known good floppy? Not a high density disk formatted to be low?
b) Pal ground mods on the daughterboard... has that been performed? That external 2MB box of yours is pretty heavy duty and not in an efficient way.
c) Expansion port connector on the A1000 real clean?
d) Female connector on your RAM expansion clean and okay?
e) bad 256k Chip RAM (extremely unlikely)
f) bad RAM in your external box (a lot more likely than a bad 1050), but try running DPaint III with only 512k and see if it Guru's right away. I don't remember how much that program requires, but if it'll load your image (hopefully a small one) up fine and doesn't crash - then you know you have RAM issues in that external box of yours. If so, hopefully they're socketed.
g) do you have an AdSpeed chip or some other accelerator in your A1000? If so, try disabling it.
