OODialog provides a FileNameDialog class and a GetFileName external function. Both of these use the same underlying Windows function and both have the same arguments.
The underlying Windows function allows for the use of a "pre-selected" file name and an initial directory to open the dialog in. The OODialog class and function do not allow the user to specify a blank pre-selected file and an initial directory. When the user tries this an error is raised.
I think that is a bug.
The fix has already been committed:
oorexx/platform/windows/oodialog oovother.c,1.3,1.4 on 2007-01-07 17:55
This bug report is just meant to document that commit, which I meant to do at the time.