act win failing with multiple excel documents

[JohnAnson]

Here's the code:
act win("test.xls")

This works fine the first time, and if test.xls was the last workbook I viewed in Excel.
However if I:
- run this command
- activates test.xls ok
- switch to another workbook in Excel (with Ctrl-F6 or Alt-tab)
- run the command again
- activates test.xls ok
- then after about 5 seconds gives the error: Error (RT) in "<macro>": cannot activate window

I am using Office 2007 SP1 on Windows XP SP2.
QM 2.2.? and 2.3.0.1 have the same behaviour/problem.
This behaviour does not occur with Word documents, ie act win("test.doc") always works without error.