Hello sowmiyass,
Basically you need to create a new View only for the popup message, then if ZAPTEST does not recognizes the OK button (You can check it by running it with the Exist method and check in the results if ZAPTEST captured its image) you need to assign to it a Relative object which may be some caption in the popup that ZAPTEST does recognize it.
If the above will not help remove the value in the “regexpwndtitle” Application’s object property and try again.
If the above will not help please attach your testing script (The *.zap file).
Thanks,
ZAPTEST Team