Thanks.
Right, I've had another look at this. The problem is only there if the file is a single line, example:
cat,cat,cat,....
If it's:
cat
cat
cat
there's no problem.
Problem file can be created by
n:=0 .. 6000/Vn:="cat"/T:=transpose of V/save V, an then try to read it.
The failure occurs at...