thanks for all the pointers Harlan. I'd misunderstodd what the
CELL("filename") function returned so I'm not sure that my
'WorksheetName' name is actually going to always return what i require.
Is there any other funtion that will achieve what I'm after?

As regards the --W=ADorksheetName&"!$A"&2+ROW()+X -- part, the X is just
a name (Row_Offset =3D 2) so it shouldn't be causing any errors. And the
2+ROW()+X should return a number everytime but I tried your sugestion
of TEXT() just in case nad it didn't solve the problem.

The problem with trying to isolate the expression where the error
occurs is that the error doesn't occur if i reference the name
directly, i.e. =3DLondon!MonthSales; the problem only comes if i
reference it using the INDIRECT function to 'build' the reference text
from data in other cells.

Thanks again
Rob