chkdsk woes

for some reason that is totally beyond me, chkdsk will not perform scheduled
disk checks on one of my disk drives.

I have 2 drives: C: (internal) and J: (external USB) (there are reasons for
this, I promise). Scheduling a chkdsk on C: works every time. Scheduling one
on J: never works.

I booted up in safe mode to avoid J: being opened, and managed to run
chkdsk. It found a cross linked file, but it does /not/ say what either of
the files in question was. Which is really unhelpful, because at least one of
the 2 files will be corrupt at this point, and possibly both of them, and it
would sort of be nice to know which!