SQL Linked Server Issue Updating AS400 tables

Hi There,

I have an SQL server through which I link to an AS/400 database. Currently, I 
can see the tables and the data in my AS400 library, but when I try to update 
data in any of the tables, I get the following error:

OLE DB provider 'MSDASQL' could not UPDATE table '[WWC]...[TABLE]' because of 
column 'COL1'. The data value violated the schema for the column.
[OLE/DB provider returned message: Multiple-step operation generated errors. 
Check each status value.]
OLE DB error trace [OLE/DB Provider 'MSDASQL' IRowsetChange::SetData returned 
0x80040e21:  Data status sent to the provider: [COLUMN_NAME=COL1 
STATUS=DBSTATUS_S_OK]. Data status returned from the provider: 
[COLUMN_NAME=COL1 STATUS=DBSTATUS_E_SCHEMAVIOLATION]].


My command is very simple:
update WWC...TABLE set COL1=1 WHERE COL2='TEXT'

the following command returns the correct data, so I know that my linked server 
is functioning to some degree at least:
select * from WWC...TABLE

And I'm sure that I've got my datatypes correct for COL1 and COL2

I am using a System DSN with the iSeries Access for Windows ODBC data source. 
Using this data source to alter the AS400 db directly (via a DTS job) works 
fine, so I think the Linked Server is adding some layer of complexity that is 
messing up my query, but I can't find any help on the issue.

If this is the wrong place to post this issue, I apologise, but can anyone tell 
me where I should go?

Thanks a lot,

Chris