I have used Audacity for a while now, using a blackstar amplifier, and had no problems. I have a fully updated windows 10 computer.
I have now purchased a “Spark Amplifier”, and now i find i can put a backing track onto Audacity, but when i press Record i get a message saying “error 9999” and cannot use the record function at all. Any help would be great.
Here are some things to try:
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Until you get basic recording to work with this unit, try turning off both software playthrough and overdubbing (Edit > Preferences > Recording)
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In the Spark Amp User Manual_0.6 released earlier today, it states:
(L) AUX In
Connect the analog output of an audio device to this port. USB audio playback and Bluetooth audio are
disabled when a connector is inserted into this port.
so make sure you have nothing plugged into this port.
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Do a Transport > Rescan Audio Devices after plugging in or making any changes to your amp.
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Make sure all of your sample rates line up. Normally you want them all to be 44100 or 48000. In Audacity, this will be in the lower left-hand corner of the Audacity screen. In Windows, type “mmsys.cpl” into the Windows search bar (by the magnifying glass). Then click on the Recording tab, select your device, click on Properties, Advanced, and set your Default Format. Repeat for the Playback tab.
I hope this helps. 
Please report back your success or failure so other people can benefit.
Thanks for the replies people, but i asked Audacity and they said to make sure the mic settings are right on my computer, they told me what to do and it has worked. So thank you for the help.