datediff error : field name not known

hello there :wave: ...

might use some help on this...

im currently using the datediff formula in my report. there seemed to be no error found if i try to check it in the formula editor but when i tried to run the report this is what i get:

This field name is not known. Error in File C:\DOCUME~1\AMALIN~1\LOCALS~1\Temp\CrystalReport {24AABB98-875C-43EA-9B76-E1B3621B5A5A}.rpt: Error in formula . 'DateDiff ("h",{vehicle.vtt_datetime_out} ,{vehicle.vtt_datetime_in} )' This field name is not known.

i can't figure out what could possibly be wrong with this...

i've been working on this for weeks now...

any help please...

thanks anywayz...