[19.1.3] The problem of ''CALC_DES_BEDHEIGHT''

When I called function ‘‘CALC_DES_BEDHEIGHT’’ and ‘‘CALL WRITE_DES_BEDHEIGHT’’ in file ‘‘write_des_data.f’’ I got a file ‘‘xx_DES_BEDHEIGHT.dat’’. But, I found that the data about bed height in file ‘‘xx_DES_BEDHEIGHT’’ is all ‘‘NaN’’. As shown in the picture:1111111111111 The first column represents time and the second column represents bed height. I hope you can help me with it, thank you!