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Editorial Team
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Asked: 2026-05-16T23:03:26+00:00

Recently deployed a project into production and have run into the Invalid postback or

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Recently deployed a project into production and have run into the “Invalid postback or callback argument” error. We haven’t encountered this in testing at all and after some research have found that the problem occurs in the following situation:

  1. Old version is published and accessed.
  2. New version is published and accessed without clearing the Temporary Files.
  3. Drop down is changed twice. (The first time everything works fine.)

The fix for the clients that have called in has been to clear their temporary internet files but this isn’t the ideal fix. Can anyone think of a reason why this would be happening and stop happening after the temp files have been cleared?

BTW: The app is ASP.NET 3.5 written in C#. We’re using a javascript call back in this particular control that’s causing this issue.

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1 Answer

  1. Editorial Team

    We didn’t want to use the “enableEventValidation=false” trick as this isn’t a consistent issue. From pretty early on, we were able to fix the issue case by case by clearing the temp files.

    After some more looking today it was suggested that we rename our js file and behold, the issue is resolved locally. Seems that each user has had our old js file stored.

    As to why it was throwing the “Invalid Postback” rather than a javascript error, we’re not sure. There are other ways of specifying the version number in the script tags but for now we opted for the rename.

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