The geosmart plugin is incompatible with the one-time-password (OTP) plugin of WordPress. The problem is that the OTP plugin does not display the challenge on the login page anymore when the geosmart plugin is activated.
A work around may be to make sure the geosmart plugin does not do something on the login page, but this incompatibility could also cause problems somewhere else.
The problem could be related to the way the geosmart plugin uses jquery. I found a bug report for OTP where the problem was the jquery handling in another plugin. The specific problem mentioned there does not seem to be the same as in the geosmart plugin, at least on the very quick look I had.
So… for now I disabled the geosmart plugin, most of the time I guessed the sequence number right, but sometimes I did not.