export to excel function is not working

i am having a problem using the export option that is available to export table data to an excel sheet.when i click the submit button, the ouput displays in the table and then when i click export i get an exception which say:...
java.lang.NullPointerException
at com.sap.ip.bi.alv.xml.ALVXMLCellCollector.collect(ALVXMLCellCollector.java:105)
at com.sap.ip.bi.alv.xml.ALVXMLDataRowCollector.collect(ALVXMLDataRowCollector.java:207)
at com.sap.ip.bi.alv.xml.ALVXMLDataTableCollector.collect(ALVXMLDataTableCollector.java:67)
at com.sap.ip.bi.alv.xml.ALVXMLTableCollector.collect(ALVXMLTableCollector.java:114)
at com.sap.ip.bi.alv.export.ALVExportXMLBase25.export(ALVExportXMLBase25.java:95)
... 87 more

and i dont get this error when i dont use "user data" connector ( a connector that contains the personal data of the user ) or when i dont click submit button to get the output.

can anyone slove this problem?



Can you tell me the procedure that you have followed..


plz elobarate your design time.




The problem is solved.It was due to a numeric field in the output of the table not due to USER DATA connector.This field is basically ´"COST" and it takes decimal values.So i just changed the value of this field to

=FLOAT(@cost) ( this converts the text string to a floating point number or you could use NVAL(@cost) even this would work )

the export function worked !!!!