If you encounter a following error, while exporting to Excel 2007 (.xlsx)
Errors were detected in file MyFileName.xlsx. Repaired Records: Cell information from /xl/worksheets/sheet1.xml part
then, probably, you are exporting string values in wrong format. The right structure in this case is
<sheetData> <row> <c> <v>99999</v> </c> <c t="inlineStr"> <is> <t>My Text</t> </is> </c> </row> </sheetData>
Note, that there is no <v> tag in <c> as it should be with numbers. Instead you have to make an inline string (<is>) tag and put text (<t>) tag with needed text in it. Do not forget to add the t="inlineStr" attribute to <c> tag.
More info can be found developer:network.