Ok, have now got it to work, & this is what I did:
I managed to get Twhirl installed without problems on my pc (which uses mandrake at present) but my laptop (using Suse) in terminal gave me the error message referred to above.
So I looked at the command line for twhirl on my pc by right-clicking the desktop icon, and the command is:
/opt/twhirl/twhirl
This was the only relevant file that seemed to be missing from my laptop (all the adobe air stuff seemed to be there). Then I copied the opt/twhirl/twhirl file from my pc to the same place on my laptop. And - excuse me while I faint - it all worked
.
Thanks Splicer for the link.