SystemParametersInfo() returns 0 randomly - c++

Question

I'm developing an application to randomly change the users wallpaper at a specific time interval. Everything works as expected, except for the occasional error of 0 set by SystemParametersInfo(), which results in the wallpaper being reset to a black screen.
The 0 error is supposed to denote the operation was successful, yet that's obviously not the case. This error does not occur every time a new background is set, but randomly. I've searched this website and many others for possible solutions.. to no avail.
void setBackground() {
dirSize = FindMaxFileNum(); //Reads num of .jpg's in the folder.
if(dirSize != -1)
{
srand( (unsigned int)time(NULL));
bgChoice = rand() % dirSize + 1;
//Ensures backgrounds don't repeat.
for(int i=0; i<=2; i++)
{
if(lastBackground[i] == bgChoice)
{ bgChoice = rand() % dirSize + 1; }
}
//Tracks the last background used.
lastBackground[bgCount] = bgChoice;
bgCount++;
//Resets the counter so we can track the last 3 bg's used.
if(bgCount == 2)
{ bgCount = 0; }
}
else
{
dwLastError = GetLastError();
ssLastError << "Error: " << dwLastError << ".";
MessageBox(NULL, ssLastError.str().c_str(), "Error!", MB_ICONEXCLAMATION | MB_OK);
ssLastError.str("");
}
ssFilePath.str(""); //Ensures the stringstream is clean.
ssFilePath << strLocalDirectory << bgChoice << ".jpg";
if( SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, (PVOID)ssFilePath.str().c_str(),
SPIF_UPDATEINIFILE | SPIF_SENDCHANGE) != 0)
{
// Refresh the desktop - cleaning of PIDL is in the WM_DESTROY message.
SHGetSpecialFolderLocation(NULL,CSIDL_DESKTOP,&pidl);
SHChangeNotify(SHCNE_ASSOCCHANGED,SHCNF_IDLIST,pidl,0);
}
else
{
dwLastError = GetLastError();
ssLastError << "Error: " << dwLastError << ".";
MessageBox(NULL, ssLastError.str().c_str(), "Error!", MB_ICONEXCLAMATION | MB_OK);
ssLastError.str("");
}
}