The MSDN CreatMutex() documentation (http://msdn.microsoft.com/en-us/library/ms682411%28VS.85%29.aspx) contains the following remark near the end:

Two or more processes can call CreateMutex to create the same named mutex. The first process actually creates the mutex, and subsequent processes with sufficient access rights simply open a handle to the existing mutex. This enables multiple processes to get handles of the same mutex, while relieving the user of the responsibility of ensuring that the creating process is started first. When using this technique, you should set the bInitialOwner flag to FALSE; otherwise, it can be difficult to be certain which process has initial ownership.

Can somebody explain the problem with using bInitialOwner = TRUE?

Earlier in the same documentation it suggests a call to GetLastError() will allow you to determine whether a call to CreateMutext() created the mutex or just returned a new handle to an existing mutex:

Return Value

If the function succeeds, the return value is a handle to the newly created mutex object.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

If the mutex is a named mutex and the object existed before this function call, the return value is a handle to the existing object, GetLastError returns ERROR_ALREADY_EXISTS, bInitialOwner is ignored, and the calling thread is not granted ownership. However, if the caller has limited access rights, the function will fail with ERROR_ACCESS_DENIED and the caller should use the OpenMutex function.