Problem: Some custom applications and tools written using ArcObjects now have errors
After installing ArcGIS 8.1, some custom ArcObjects applications and tools may have errors.
Changes were made to the type library for ArcObjects between ArcGIS version 8.0.1 and 8.1.
Most of the changes will not affect your applications as they were made to remove inadvertently included data types. A few changes might affect your applications.
Solution or Workaround
Recompile your applications with the 8.1 libraries. The errors should go away.
For more information, see "Changes to 8.0.2 Data Types at 8.1" in the Technical Documents section of the ArcObjects Developer Help.