I’m sorry, I started getting this problem and rashly deleted all of my testnet3 folder, so I don’t have the log or my original coins anymore. I’ve mining new coins overnight, so I’ll try it again very soon and let you know what happens.
Update: I’m not having this error anymore, but I also don’t have as many separate notes as before (around 40 before, only around 4 now), which I think might have been related.
When I was having this error, all the coins were what I had mined, then sent to my private address. When I was sending some of the coins to my private address, I would set the amount on z_sendmany as 0.1, and because of the way newly mined coins behave (I don’t know why exactly), all of the original transaction was sent to the private address (in two parts, 0.1 and the remainder). This may or may not be relevant, but it did increase the number of notes. Anyway, just a few details if you’re interesting in trying to reproduce this error.
Update 2: I’ve since mined many more coins, and successfully completed similar transactions to those above (with more individual notes than above) on the same system without any errors, so I simply don’t know what was causing this.