Hi Rachel,

How to deal with it depends on why the grids are different.

What are the differences between datasets ck_l1 and ck_r1?

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For example, I did a quick Search (to the right of "New Topic")
on the error string "perhaps you could make your datasets match"
and found issues dealing with obliqueness, among others:

<[afni.nimh.nih.gov];
<[afni.nimh.nih.gov];

But we can only guess why this is happening to you. Either
describe your datasets in more detail, or maybe give us some
of the '3dinfo' output on them. Be careful to remove any
subject names from the output. If you are unsure about the
subject info, send it to me via private email.

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Also, note that 3dvolreg complains about the -tshift option.
Apparently there is no slice timing in ck_r1+orig.

- rick