Error while using vl_covdet

While using the vl_covdet function to form descriptors for given input frames(custom frame), this is the error returned by the function:

Error using vl_covdet
FRAMES must be a palin matrix.

Can anybody help me debug this error? This is a new error and it came after I made just a couple of changes to the frame being fed to this function. The change involved changing the values of a particular row.

I have no clue what to do next