Unable to find control id on panel tab change.

Unable to find control id 'txtDOJ' referenced by the 'ControlToCompare' property of 'cvtxtEffectiveFrom'.

Description: An unhanded exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Web.HttpException: Unable to find control id 'txtDOJ' referenced by the 'ControlToCompare' property of 'cvtxtEffectiveFrom'.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.

I am phasing this problem during accessing control id from Ajax TabContainer. Here I create multiple tab, and i want to access data from first tab to another tab. But this is throwing exception of "Unable to find control id."