Thanks for the fix, now it is working for the erp files without any error!
That's how I had imported though, right click on the subject folder>"Import MEG/EEG > EEG: erpfiles".
I think what happened was I saved my whole workspace by mistake as the DatMat file so my raw (was open via EEGlab) file got saved along with the DatMat....I should have realized this when I saw the file size.....