iraf.net

I started to study how to use iraf,
but when I use flatcombine, it says

ERROR: HDMGETR: No value found
"ccdproc (ims, output="", ccdtype=ccdtype, noproc=no"
line 38: ccdred$flatcombine.cl
called as: 'flatcombine (mode=h)

but, I don't know what this error means.
zerocombine and darkcombine worked well but flatcombine didn't.

I use flatcombine under this parameter setting

input = @Flat.list
output= FLat
combine=median
reject= avsigclip
ccdtype=
process= yes
subsets= yes
clobber= no
scale= mean
statsec=[51:460,51:460]
nlow= 1
nhigh= 1
mclip= yes
lsigma= 3.
hsigma= 3.
rdnoise= 15
gain= 2.2
snoise= 0.
pclip= -0.5
blank= 1.
mode= ql

and in the @Flat.list, there are u, v, b filter flat images so I used subset.
If there is anything you say needed to know, I will attach it.
Thaks

Generically, the error means that some header parameter was not found when CCDPROC was run (because you had the process=yes parameter set), commonly this is the exposure time ('exptime') keyword. If you do have an exposure time in the header, it may be that the SETINSTRUMENT task needs to be run to get the right header values, or the CCDPROC task has parameters set from a previous run that doing an "unlearn ccdproc" might clear up. If the problem continues, please post an image header from one of the flat files.