I guess all who suggested not to use the computed column were right.

After I added the computed column with the following formula:

case when ([lMvNeeded] = 1) then ([iMvQuantity] + [iMvAdditional]) else [iMvAdditional] end

all stored procedures that queries this table returns the following error message:

Server: Msg 8101, Level 16, State 1, Procedure webforms_ipo_Section013Select, Line 63
An explicit value for the identity column in table 'ipo_reagent' can only be specified when a column list is used and IDENTITY_INSERT is ON.

As soon as I remove the computed column SP completes OK.

Any idea why computed column is causing that behavior ?

Thanks again.
Daniel