#4 Collection was modified error

[Anonymous]

Netspell is a great product and works well but about
twice a day I get the following error:
Collection was modified; enumeration operation may not
execute.
the stack trace is
System.Collections.ArrayListEnumeratorSimple.MoveNext
() at NetSpell.SpellChecker.Spelling.Suggest() at
NetSpell.SpellChecker.Spelling.SpellCheck(Int32
startWordIndex, Int32 endWordIndex) at
NetSpell.SpellChecker.Spelling.SpellCheck() at
spellcheck.Page_Load(Object sender, EventArgs e) at
System.Web.UI.Control.OnLoad(EventArgs e) at
System.Web.UI.Control.LoadRecursive() at
System.Web.UI.Page.ProcessRequestMain()
Any ideas as to why this would occur?