Below error is what iam getting. Actually in Public Section, Methods are defined and from those there is a dump saying "Type 'IBST_A_BUF_TAB' is unknown" from one of the methods 'CHANGE'. I did version comparison with all systems but no difference exist . So what can I do in this case?
You say that the same error exists in a non-upgraded system. Yet you also say this issue only came up after the upgrade of one system. If the same error exists in the non-upgraded system, then presumably it exists in your upgraded system before the upgrade.
You didn't answer my question about where the class comes from. For example, if an application is developed in ERP and great care isn't taken, if you try to import that class into a BW system, you'll get many errors concerning missing objects.
In any case, the resolution is the same: