nlapiSubmitField does not seem to work with location????

Hi-

I am writing a script to update the location field on some records. If I put the following two lines into the script the 'memo' field will update, but the location will not...

nlapiSubmitField('estimate', 3813, 'location', 3, false);
nlapiSubmitField('estimate', 3813, 'memo', "Testing...", false);

What is more annoying is that if I put the following I get a "This location is not valid for subsidiary X" error if I put:
nlapiSubmitField('estimate', 3813, 'location', 4, false);

Furthermore, if I put the following I get a "Invalid Reference For Location" error if I put:
nlapiSubmitField('estimate', 3813, 'location', "Brisbane", false);

What gives? Can location not be updated by script?? It is listed in the reference guide as a scriptable field...