AL_INVALID_OPERATION can occur for a few reasons ...a) Trying to alSourceQueue one or more Buffers on a Source that already hasa Buffer attached to it using alSourcei AL_BUFFER. (If you are streamingdata to a Source you should always call 'alSourceQueue' to add Buffers tothe Source.)b) Trying to alSourceQueue one or more Buffers on a Source that havedifferent Formats or Frequencies. (All Buffers in a single Source Queueshould have the same Format and Frequency).c) Running out of voices. This is possibly the most likely issue -because it is dependent on the soundcard you have installed. (If you areplaying a mixture of Stereo and Mono Buffers then you need to be carefulwith your Source management because a Source playing a Stereo Bufferrequires two hardware voices instead of one for a Mono Buffer. If youknow how many Stereo samples you need to play simultaneously then you canprovide that information as a Context Creation 'hint' so that the AL devicereduces the number of Sources that can be generated accordingly.