That was just an example, however i've now found my code does work -
the reason i thought it was not working is that it doesn't update the
text in the controlsource box in the properties window.

So before my code the control source of textbox1 is set to Sheet4!G1
I run my code to set it to Sheet4!H1
The textbox now links to Sheet4!H1(i have tested this by putting in a
value etc) however the controlsource in the properties window still
shows Sheet4!G1

I know this is very strange.....