SVD did not converge. SPM 1st level

Hi all,
<span style="white-space: pre;"> </span>have you ever suffered such bug in only few subjects when doing SPM 1st level?
It seems the matrix design has some trouble, but I have no idea how to solve it.
pls help!
Thansks!<span style="white-space: pre;"> </span>
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Mapping files : ...done
Calculating globals : ...done
Saving SPM configuration : ...SPM.mat saved
Design reporting :   - Failed 'fMRI model specification'
Error using svd
SVD did not converge.
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