no second gear

I have a 04 freelander td4 sport, it was working great until last week, then when i was out and about it wouldnt let me select second gear unless the car was idle, so flushed the gear box and replaced the oil, worked perfect for 2 days and now back to square one, does anyone have any ideas?, there is no clunking, grinding and all other gears including reverse are fine,

thanks

Anyone??????