If you are using the spell checking tool with Adobe Reader 8.1.x you may experience an application crash and error message like the following:
The crash usually occurs when you enter text in a text field that is not already in the dictionary. You then right-click on the text field to bring up the spell checking context menu:
Without selecting any of the options in the spell checking menu, you click another field on the form. Then the crash occurs.
This crash has been fixed in Reader 8.2.x and in Reader 9. Upgrade to these, or later versions to solve this issue.