This error means either:

a) you used these api keys somewhere else with a too big nonce, so now we can't use these keys for the api import anymore. In this case please set up a new key and secret only for us
or
b) you just ran an import, had lots of trades and to get them all we had to increse nonce a lot after all calls. In that case, you can just wait some time (up to 1-2 days in some rare cases)