I followed exactly instruction Converting LHCoin_b tokens into LHCoin in myetherwallet and still got this error message.
I converted my tokens without any problems. Most likely you are doing something wrong. There are no technical problems. The only problem is that the tokens are not automatically displayed in the MEW wallet. You need to add them manually
At first I could not convert for a very long time because in the very last step I had to put the number 0 and I made a token count.