OLAP parameters - optionally exclude members of a group

Question

I have a report that shows activity for members of one of more workgroups.  There's a parameter for that and it works correctly.  The business now wants to exclude a few members of a few workgroups.
In the query designer, if I don't have the Not Equal filter set as a parameter, the query works even if no users are selected - which is the default behaviour.
However when I make it a parameter, it will demand at least one workgroup member name (and the list is just the members of the selected workgroups).  I have the default value set to {[WorkgroupDim].[User].&[]} and the parameter set to allow blank
values.
Right now, the dataset query uses a not equal operator.  I could change it to Equal, but that would be a maintenance nightmare as new members are added to workgroups.  
The report is being used as the master version for a lot of linked reports, each using its own list of one or more workgroups and excluded names.
Tim 

Answer 1

The only thing I can still think of is file permissions.
If the system has recently been restored or Redo Log recreated, check the file permissions and ensure that Oracle has Read and Write Access to the Directory and Files.
At least the file permissions on the directory and files should look something like this example
$ls -l /sampledb/redo0/oradata/sampdb/
drwxr-xr-x oracle oinstall 4096 19 May 17:46 redo
$ls -l /sampledb/redo0/oradata/sampdb/redo/
-rw-r----- oracle oinstall 524288512 27 Oct 15:07 redo101.log
$ls -l /sampledb2/redo0/oradata/sampdb/redo2/
-rw-r----- oracle oinstall 524288512 27 Oct 15:21 redo102.log
$ls -l /sampledb3/redo0/oradata/sampdb/redo3/
-rw-r----- oracle oinstall 524288512 27 Oct 15:33 redo103.log