its proberly me at fault here on this one i hope you can help out,i drive a man tga xxl and the time on the tacho bit above your head were you put the card in wont stop flashig and its got a 
next to it. with no manual to look at icant stop the bleeding thing,we also have two new erf,s with the same kind of set up but are diffrent if you know want i mean, any ideas
i always found that if i remove both tachos then close it it recalibrates itself try that i may be wrong someone will put u right!! 
what make of tacho is it ,look on the website from the maker and you will
find hopefully a working description of the problem also if not by putting the make +model some one may be able to put you right,
don,t now the make but i will have a look on tuesday
You may find in the tacho section of the drivers hand book a series of fault finding and solving procedures.
acarlin1:
i always found that if i remove both tachos then close it it recalibrates itself try that i may be wrong someone will put u right!!
Works for me too.
Take both cards out and any blank protective discs. It will then reset the time from the computer and reset the tacho.
I need to do this every couple of months
It usually means that it wants to adjust the time and it can’t do that with a disc, or discs in it. Remove all discs, then close the drawer and you will hear it whirr a bit then the fault should be gone.
It could be that the vehicle has had the batteries disconnected while in for a service and thime is now a little out, the tacho head usually sets the dashboard clock as well and this maybe what is needed.
With these newer style heads you should not keep a disc in the 2nd man position unless the vehicle is double manned, for normal one driver operation leave the 2nd driver slot empty at all times.
You could try shutting all the windows, get out and close it all down. Then get back in, re-boot and re-open the windows. Seems to work for Micro$oft 