>> "P.S. a) I am using the latest 2.6.18 bundle"
I don't know what that means. We've never released a 2.6.18 version of TurboActivate. The current version is 4.0.9.6.
More information: https://wyday.com/limelm/api/ta-changes/
>> "Tried all the things as stated, but success is not gained. Could you shed some light on this please."
More information is needed. If it's only happening on this one customer's machine then they might've messed with the files. Have them re-install your app. Then, have them follow all of the methods the make systa executable on Unix: https://wyday.com/limelm/help/using-turboactivate-with-adobe-air/