'View definition has been changed' is the message appeared when running my program . what can I do to resolve it

In addition to what Sergey and Dan have told you, you should also look for things like this in the field list of your view definition

NVL( MyTable.MyField, SPACE( 30 ) ) AS MyField

If MyField in MyTable happend to be defined as C( 35 ), it will also cause this error.