[Dev-C++] Access Violation (Segmentation Fault)

When I debug this program, I get "Warning: An Access Violation 
(Segmentation Fault) raised in your program."  When I get this error 
msg, I end up in stl_construct.h.

----------------------------------------------------------------------------------------------------------------------------
int Range=0;
int PreviousRange=0;
vector<int> Groupset;        // subscripts/pointers to Groupset ranges
ofstream DGroupset("W:\\AAAnalysis\\DGroupset.txt");
ofstream DWDRlist("W:\\AAAnalysis\\DWDRlist.txt");

....
int main()   {
....                              
        if (Mtglist[i].substr(0,1) == "*")    {                       
            if (Mtglist[i].size() == 8)    {                           
                Groupset.push_back(Range);           
<=======================> Here's the stmt that yields the error.
                DGroupset << Range << endl;
                DWDRlist << Mtglist[i] << endl;      
                PreviousRange=Range;
                TWDR++;
            }
           }
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I know that you always want to see the entire program, but it is over 
300 lines long, so please let's see if anyone can see anything glaringly 
wrong with this, okay?

At the moment of error, Range = a valid integer.
DGroupset is merely a disk image of the vector so I can see what's going on.
I have checked if "Range" is a reserved word (it is not).
I have checked if a vector<int> needs any special handling (it does not).
I have chkdsk'ed the partition.

What could cause this?  What are some causes a Segmentation Fault?

TIA,
Ken