In my program I use the Running Object Table (ROT) to ensure only one instance of my program is running. Since I "inherit" that code from a developer who unfortunately left the company, I am the poor guy to solve the problems. The code works fine, but we have 3 customers (out of 39,000) who will get an AccessDeniedException. Every customer runs the software in user mode.

Any suggestions what could be wrong?

bool retVal = false;
IMoniker[] arrMoniker = new IMoniker[1];
IBindCtx bindCtx = null;
string displayName;
int hResult;
int mkSys;
Guid clsidRot;
bool guidCompare = false;

IntPtr number = IntPtr.Zero;
moreObjectsListed = false;
objectFromRot = null;

try
{
    // check the objects in the running object table for fitting the specified class id
    while ((retVal == false) && (0 == enumMoniker.Next(1, arrMoniker, number)))
    {
        hResult = CreateBindCtx(0, out bindCtx);
        if (hResult == 0)
        {
            arrMoniker[0].IsSystemMoniker(out mkSys);

            if (mkSys == 4)
            {
                try
                {
                    // the display name is the class id of the object in the table
                    // --> AccessDeniedException raises here <--
                    arrMoniker[0].GetDisplayName(bindCtx, null, out displayName);
                    clsidRot = new Guid(displayName.Substring(1));  
                    guidCompare = clsidRot.Equals(clsid);
                }
                catch(Exception) {}

                // an object with fitting class id was found
                if (guidCompare == true)
                {
                    rot.IsRunning(arrMoniker[0]);
                    rot.GetObject(arrMoniker[0], out objectFromRot);
                    retVal = true;
                }
            }
        }
    }
}
finally
{
    if (arrMoniker[0] != null)
    {
        moreObjectsListed = true;
        Marshal.ReleaseComObject(arrMoniker[0]);
    }
    if (bi
c# running-object-table
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