Constant Issues with Online Check-In

I fly with British Airways often for work and always seem to encounter problems with their online-check in system. This has happened numerous times and results in having to be delayed by waiting in queue's at the airport. I am able to check in online effortlessly and easily with every other Airline company, however with BA I always have problems with the following error message:<br> I know my booking reference & details are correct as I am a frequent flyer. Please assist. <br> <br> Error<br> Sorry, We are unable to find your booking. Please check the following:<br> Booking Reference - This is a series of six letters and numbers.Help me find my booking reference.<br> Last name of passenger - this needs to be entered with the same spelling as on your travel document<br>