Rebuild index failed

I scheduled a maint plan to rebuild index. All table's indexes are successfully built except for one table. The error message I got:

Failed:(-1073548784) Executing the query "ALTER INDEX [Index_name] ON [dbo].[table] REBUILD WITH ( PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, SORT_IN_TEMPDB = OFF, IGNORE_DUP_KEY = OFF, ONLINE = ON )
" failed with the following error: "Online index operations can only be performed in Enterprise edition of SQL Server.". Possible failure reasons: Problems with the query, "ResultSet" property not set correctly, parameters not set correctly, or connection not established correctly.

Can someone tell me what the problem is and how to fix it? Thanks.

I am assuming you are using the Enterprise Edition of SQL 2005?|||

We are using Enterprise Edition. All other tables can be reindexed. This is the only table has problem. And this is not a big table. The indexed column is nvarchar(50).

Any ideas?