Update statement shows error while compiling in forms

Question

i have the following query which works fine through TOAD,but in forms while compiling it gave error:
"too many declarations of 'DECODE' match this call".
Can any body suggest me a workaround for this query to avoid this error.
UPDATE job_headers_web
SET draft_release_date = SYSDATE,
    jbhwb_draft_approval =
                 DECODE (jbhwb_draft_approval,
                         NULL, jbhwb_draft_approval,
    jbhwb_draft_approval_date =
            DECODE (jbhwb_draft_approval,
                    NULL, jbhwb_draft_approval_date,
    jbhwb_draft_approval_logon_id =
        DECODE (jbhwb_draft_approval,
                NULL, jbhwb_draft_approval_logon_id,
WHERE reference = 'IRef487'

Answer 1

thanks all.esp Dave & Gerd ,for giving me the possible solution...finally i got it right
it was the problem with the date field
so i have modified my query :
UPDATE job_headers_web
SET draft_release_date = SYSDATE,
    jbhwb_draft_approval =
                 DECODE (jbhwb_draft_approval,
                         NULL, jbhwb_draft_approval,
    jbhwb_draft_approval_date =
            DECODE (jbhwb_draft_approval,
                    NULL, to_char (jbhwb_draft_approval_date),
    jbhwb_draft_approval_logon_id =
        DECODE (jbhwb_draft_approval,
                NULL, jbhwb_draft_approval_logon_id,
WHERE reference = 'IRef487'