As of TM1 10.2 the tm1web will no longer support Excel 2003 .xls files.
Fear not though as there is a conversion tool available.
Just go into Architect/Perspectives and right click on your .xls file to find a conversion tool.
Mine converted all fine without error.
For more details see: http://pic.dhe.ibm.com/infocenter/cbi/v10r2m1/index.jsp?topic=%2Fcom.ibm.swg.ba.cognos.tm1_op.10.2.0.doc%2Fc_tm1_web_converting.xlsworksheets.html
