I am glad to have been able to help.
Another option, that avoids potential internationalization problems, is:
call GroupWise.ViewOpen(vwtCalendar, TRUE, "")
Regarding the date format issue, I am not sure what you mean by ‘wrong under certain circumstances.’ As I understand it, GroupWise always uses the formats specified on the Format tab of the Date Time Options dialog. If the default is the US date format, this is a flaw; I would expect the default format to follow the System format.
Please see your Forum thread GroupWise vs system date format for further comments on the date format.