Dear All, I still cannot solve the error (see attached printed pdf file). Can somebody give me some advice? I have also attached my data file in Excel and text formats for your reference. I have already assigned the y1,y2,....x1,x12,z1,z2.....z14 as V1....V23 but still can't work. Please try out and advise. Thanks. Andy -------------- next part -------------- A non-text attachment was scrubbed... Name: result.pdf Type: application/pdf Size: 29819 bytes Desc: not available Url : https://stat.ethz.ch/pipermail/r-help/attachments/20060205/54ab9bc1/result.pdf