Why does this ring operation occasionally give an error?

Question

I am using LabWindows/CVI, and I created a low-level ring acquisition. It works normally at first, but if I stop it and start a few times (does not always happen on the first stop / start cycle), then I get the error:
NON-FATAL RUN-TIME ERROR: "Dalsa.c", line 2716, col 13, thread id 0x000012A4: Function imgSessionCopyBuffer: (return value == -1074397014 [0xbff600aa]).
The requested buffer has been overwritten and is no longer available. It occurs on the second line of the following code:
(2715) imgGetAttribute(Sid, IMG_ATTR_LAST_VALID_BUFFER, &currentRingBufNum);
(2716) imgSessionCopyBuffer(Sid, currentRingBufNum, (uInt8*)pixel_address, FALSE);
I stop my acquisition by :
imgSessionAbort(Sid, &ringBufNum);
Then I unlock my ring buffer, dispose each element, and finally dispose of the buffer list. The next acquisition starts by creating a buffer list, creating and allocating each element, locking the buffer list, and configuring the session to use that buffer list. I am NOT closing the session or the interface, I only do that upon quitting my program. Why do I get this error??
Buffer creation code:
//Create a buffer list
imgCreateBufList(NUMRINGBUFFERS, &Bid);
//Find out how big the buffers should be in memory
imgGetAttribute(Sid, IMG_ATTR_BYTESPERPIXEL, &bytesPerPixel);
bufSize = AcqWinWidth * AcqWinHeight * bytesPerPixel;
//Create the ring buffer
for (i = 0; i < NUMRINGBUFFERS; i++)
//Create individual buffer elements
imgCreateBuffer(Sid, IMG_HOST_FRAME, bufSize, &ringBuffer[i]);
//Now tell the buffer list where these buffers are by populating them into the Buffer List Bid
imgSetBufferElement(Bid, i, IMG_BUFF_ADDRESS, (uInt32)ringBuffer[i]);
imgSetBufferElement(Bid, i, IMG_BUFF_SIZE, bufSize);
//If we are still filling the buffer, this configures the current buffer on the list to move to the next buffer
//If we are configuring the last buffer in the list, this buffer will now loop to the first element when it is filled
bufCmd = (i == (NUMRINGBUFFERS - 1)) ? IMG_CMD_LOOP : IMG_CMD_NEXT;
imgSetBufferElement(Bid, i, IMG_BUFF_COMMAND, bufCmd);
//Locks the buffers in the buffer list
imgMemLock(Bid);
//Configure the session to be a ring acquisition using our buffer list
imgSessionConfigure(Sid, Bid);
Buffer disposal code:
//Unlock the ring buffer memory
if (Bid) imgMemUnlock(Bid);
//Free the ring buffer memory
for (i = 0; i < NUMRINGBUFFERS; i++)
if (ringBuffer[i] != NULL)
imgDisposeBuffer(ringBuffer[i]);
ringBuffer[i] = NULL;
//Free the buffer list
if (Bid) imgDisposeBufList(Bid, FALSE);
Bid = 0;

Answer 1

I have made some progress on narrowing the error down, but it still remains a large problem. Error trapping allows me to avoid the necessity of rebooting the system. However, I must still close and re-open my LabWindows application in order to successfully acquire from a ring.
I have narrowed the problem down to the buffer index provided by "imgSessionStatus" : on the acquisition that throws an error, it returns "-1" as the current buffer index. Why is this??
I have modified my program so that I close both the session and the interface when I hit "Stop", and yet I'm still receiving this problem when I attempt to restart the ring acquisition after stopping.  I have also started using "imgStopAcquisition" instead of "imgSessionAbort".  What could I not be properly resetting after I free, dispose and close the buffers, buffer list, session and interface?  Obviously the resource is being properly freed upon application closure, so I must be missing something ...