I am getting below expression error when trying to access Task report by the ba

It seems your expression is trying to index the first element of a list but the list is empty:

java.lang.ArrayIndexOutOfBoundsException: Invalid index (1) for list: valid range is empty

maybe because this user doesn't have tasks and your expression doesn't handle this use case properly

but same report is working for the Admin user

If the Admin user expression returns an array that does have data then that's why this would work. Remember, the error shows that for the basic user the expression is returning an empty array somewhere and you're trying to get item 1 out of that empty array.

When I am accessing report by the basic user, the getportalreportdatasubset is not returning any data.
My basic user is member of App_Viewer group. and same role is assigned to the viewer group config of tempo report. The security of portal report folder is also set to the administrator for the same role.
Any pointer!!!

Maybe you're not passing the right context for the report or the user does not have tasks.

Thanks Eduardo..