[amelia] error: inv_sympd(): matrix appears to be singular

Hi, I ran something similar to: DataImputed <- amelia(x=GroupData,incheck=FALSE) GroupData is several thousand observations with about 4 dozen variables. After iterating over a thousand times with this error: error: inv_sympd(): matrix appears to be singular It ended with: Error in emarch(x.stacked$x, p2s = p2s, thetaold = NULL, tolerance = tolerance, : BLAS/LAPACK routine 'DLASCL' gave error code -4 I searched online for both of these error messages but didn't find anything useful. Do you have any idea what might be going on, or how to fix it? Thanks for any light you can shed!