The problem seems to be gone. I tried with generating lod with one last time, it perfectly got generated and there's no CTD. However, this time I reduced the settings to 512 from 1024. Anyway, many thanks for the help. Btw, I had a question. Is it possible to generate terrain lod through x-lod gen of a heightmap larger than 2048x2048 (i,e 4096x4096) with the same lod as tamriel.lod?