Вот какие результаты дал поиск по Вашей ошибке в КВ. Поскольку мне неизвестен номер версии и примерный вид запроса, то разбирайтесь со всем этим добром дальше сами. Определите, какой из описанных ниже случаев более всего похож на Ваш, и примите меры, указанные в resolution.
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1 Q302825 - FIX: Complex Join Query with Views and Redundant Tables May Cause Error 8623
2 Q214818 - FIX: UPDATE of Table Column with a FOREIGN KEY Constraint May Fail with Msg 8623
3 Q225141 - FIX: SELECT Statements With UNION May Cause Error 8618
4 Q235401 - FIX: 8623 Error with INSERT-SELECT when Nullable Clustered Keys not Referenced
5 Q260652 - PRB: Nested Loop Join That Uses A "BOOKMARK LOOKUP ...WITH PREFETCH" May Hold Locks Longer
6 Q264005 - FIX: Error Message 8623 Occurs If You Use INSERT-SELECT with NOT IN or NOT EXISTS Keywords in Subquery of the WHERE Clause
7 Q274329 - FIX: Optimizer Slow to Generate Query Plan for Complex Queries that have Many Joins and Semi-Joins
8 Q274467 - FIX: Queries with TOP N PERCENT in Subquery May Fail with Error Message 8623
9 Q286255 - FIX: UNION Query Returns Internal Query Processor Error Message 8623
10 Q287515 - PRB: Execution Plan & Results of Aggregate Concatenation Queries Depend on Expression Location
11 Q290212 - INF: List of Bugs Fixed in SQL Server 2000 Service Pack 1 (1 of 2)
12 Q295025 - FIX: UPDATE statement unable to come up with an Execution Plan, Appears to be Infinite Loop in Optimization
13 Q294787 - FIX: Update Plan with User Defined Function May Fail to Find a Plan
14 Q294873 - FIX: Modifications to an Indexed View Built with Aggregates May Give Incorrect Results
15 Q299652 - BUG: Select with order by clause against table with 256 varchar columns on SQL 2000 fails