converting label format: nifti - freesurfer - MNE

Hi,

I'm making custom ROI labels using FSL's flirt, and converting them into .label format with mri_cor2label. This process is successful since I could overlay my new ROI labels on MRI images (e.g. brainmask.mgz) in tksurfer. However, when I try to overlay them onto inflated surface in mne-analyze, I get this error: some label vertex indexes are out of range.

Then, if I open a label in tksufer and save it (in tksurfer, without changing anything), I'm able to overlay the label in mne-analyze. I'm puzzled why this is, and am wondering if there is a way to skip this intermediate (tksurfer) step.

I'd appreciate any suggestions! Akiko