If you receive an INPUT_VALIDATION_ERROR message then the most likely cause is that your Betfair password contains some "invalid" characters. It appears that certain punctuation characters (like the # symbol) can cause log in problems when using the standard API log in.
You have two choices:
1. Amend your Betfair password on the Betfair web site and then log in using the new password.
2. Follow these steps:
a) Ensure that TBE is not running.
b) Go to the C:\BetDynamics\TheBetEngine folder and rename the "NoTwoFactor.cfg" file to "TwoFactor.cfg".
c) Start TBE.
A login dialog box showing only a single entry (your TBE account name) is shown. Enter your TBE account name and click on Login. A Betfair web page should now be displayed. Enter your Betfair username and password into the web page.
Please note: using this method does NOT allow TBE to run continuously and it will NOT rollover automatically at midnight.