Our company is working on MIDI devices that are configured using SYSEX messages. I am seeing a weird behavior with Windows 7 and Windows 8. I send 5-10 SYSEX messages to the device and receive the expected responses, then for the next 20-300 messages the responses do not come back. After sending those 20-300 SYSEX messages the response start coming in. I have placed a Beagle (USB logger) on the line and setup USB logging in windows. From what I see the responses are being sent from the device. The response size of the SYSEX messages is less than 128 bytes (around 50 bytes on average). I have tried using the WindowsMM libraries and the KS libraries and they both exhibit the same behavior. My felling is that the issue lies in the USBAudio.sys driver. This device works on Windows XP, Mac, and iOS. I have not tested on any other platform. Any help would be appreciated. Thank you. Timothy Knudtson iConnectivity