Error with Bet when processing two people at once but not when processing seperately

Hi,

I'm encountering a strange error with the bet procedure. That is, I tried to process two persons at once and then I get an error with bet when processing the second person. But what I don't understand is that if I process the two persons seperately, it all works fine for both persons. Here is the error I encounter:

0.739118 for pre-processing
0.140905 for normal computation
0.658801 for search along normal
0.052821 for checking self-intersection
0.517607 for output
Error using nifti/subsasgn>assigndat (line 367)

Unknown filename extension (.gz).

Error in nifti/subsasgn>fun (line 76)
            obj      = assigndat(obj,val);

Error in nifti/subsasgn (line 20)
        obji    = fun(obji,subs,val);

Error in y_Write (line 61)
NIfTIObject.dat=dat;

Error in y_Call_bet (line 47)
    y_Write(Data,Head,OutputFilename);

Error in DPARSFA_run>(parfor body) (line 1400)
            y_Call_bet(T1File, OutputFile_Temp, '');

Error in DPARSFA_run (line 1372)
        parfor i=1:AutoDataProcessParameter.SubjectNum

Error in DPARSFA>pushbuttonRun_Callback (line 1670)
    [Error]=DPARSFA_run(handles.Cfg);

Error in gui_mainfcn (line 96)
        feval(varargin{:});

Error in DPARSFA (line 30)
    gui_mainfcn(gui_State, varargin{:});

Caused by:
    Error using nifti/subsasgn>assigndat (line 367)
    Unknown filename extension (.gz).
 
Error while evaluating uicontrol Callback
 

Thanks in advance!