How can I increase the time allowed for a View Export operation in DOORS NextGen 6.0.3?

I am trying to export a view from DOORS Next Gen 6.0.3 which has approximately 4800 rows of requirements data to XLS or XLSX format. When I only include "simple" attributes (i.e. those with a single value), the export works, however as soon as I include a column containing an attribute that has multiple values, the export fails silently.   I can only export approximately 1800 rows with multiple-value attributes included.

I've noticed that the "waiting for <doors URL>" message at the foot of the screen disappears after precisely 2 minutes leading me to believe I'm hitting a timeout limit.

I've increased both the query timeout and Web UI timeout parameters to above 2 minutes, however the "waiting" message still goes after 2 minutes.  

I've also tried increasing LQE timeout properties (though I don't know if they are relevant in this context) - again with no result.

I restarted the underlying Websphere server after each property change to restart the Rational applications.

Any suggestions appreciated

Regards, Jim.