** This issue is addressed in ArcGIS 9.0 Service Pack 2 (SP2) **
when creating a TIN or adding features to an existing TIN the following error message is reported in some data specific cases:
"Internal process error"
This is a known issue.
Solution or Workaround
** This issue is addressed in ArcGIS 9.0 Service Pack 2 (SP2).
Click on the link in Related Information below and download Service Pack 2, if necessary. **