Without seeing your error message, and with limited knowledge of you database, it is difficult to tell.
What I would do is pick the line apart, and use the debugger to single step through each stage:
DataRow dr = objDTTabCustDtl.Rows[0];
object o = dr.ItemArray[25];
string s = Convert.ToString(o);
At each stage, see what you have, and try to work out what the next stage should produce before you move through it.