I have a situation with a c# application attempting to store and look up
some unicode value in an NVARCHAR.  Apparently the system is having issues
dealing with some Unicode values on inserts or lookups.

My tables:

/* table containing terms */
CREATE TABLE [dbo].[TermTable] (
[TermID] [int] IDENTITY (1, 1) NOT NULL ,
[Term] [nvarchar] (256) COLLATE SQL_Latin1_General_CP1_CI_AS NOT NULL
) ON [PRIMARY]

/* table containing many-to-many relation from terms to something else, with
a Unique index on FID and TERMID  */
CREATE TABLE [dbo].[TermRelTable] (
[FID] [int] NOT NULL , /* foreign key to related item */
[TermID] [int] NOT NULL
) ON [PRIMARY]
GO

Code uses SQLCommands and parameters, with the statements prepared before
execution.

Pseudocode
int foreignkeyid;
string [] Terms;
foreach term in Terms
   Lookup term in TermTable, get TERMID
   if not found, insert row in TermTable with Term, and get the
SCOPE_IDENTITY into TERMID
   insert row in TermRelTable with foreignkeyid and TERMID.

For some sets of data values (this is just one of the failing sets) the
operaiton fails.

Assume Terms[0]='xpl'
Assume Terms[1]='xpl?' where the last character is 0x0224

When the system attempts to see if the second term is in the TermTable, it
finds the FIRST term - and the subsequent insert into the TermRelTable fails
with an integrity constraint.

the SQLProfiler Trace of the relevant operations :
-----------------------------
exec sp_execute 2, @Term = N'xpl' // look up XPL

exec sp_executesql N'INSERT INTO TermTable(Term) VALUES (@Term);Select
SCOPE_IDENTITY()', N'@Term nvarchar(256)', @Term = N'xpl'  // didn't find
it - insert it into TermTable

exec sp_execute 2, @FID = 192239, @TermID = 1550945 // insert row into
relationship table

exec sp_execute 2, @Term = N'xpl?'  // look up term in TermTable, expecting
to NOT find it

exec sp_execute 2, @FID = 192239, @TermID = 1550945    // it found the OTHER
term - and attempts to insert an entry in the TEMRELTABLE - generating an
exception.
--------------------------------------

So - what do I look at to get this to work?  I do not control the source of
the terms - they can come from anywhere and so can contain any unicode data
value (this one happens to be a latin capital letter z with hook)

Note : The c# code does not have actual char constants - the characters are
read from a text file (using a StreamReader).  I included the two
assumptions to show the data values in particular that the application was
having an issue with.

I know that the characters ARE read from the file as Unicode - as I can
watch them as they're assigned to be the parameter which is sent to the dB
command and shown in the SQLProfile log.

sp_execute 2, @Term = N'xpl'
sp_execute 2, @Term = N'xpl?'

where the ? character exactly corresponds with the position of the value
0x0224 in the string passed to the SQLParameter.

(already posted in microsoft.public.sqlserver.programming - but it was
suggested that I cross-post to here)