I get the message "Undefined function in an expression."

Microsoft Office Access 2003

A control in a data access page or a form that is open in PivotTable view or PivotChart view can contain an expression that uses a Microsoft Visual Basic for Applications (VBA) function. However, the expression will generate an error unless it appears on the following list.

Note  This limitation doesn't apply to expressions in tables, queries, views, stored procedures, or user-defined functions that you have opened in PivotTable or PivotChart view.

ShowA - C

ABS ARRAY
ASC ASCB
ASCW ATN
CBOOL CBYTE
CCUR CDATE
CDBL CHOOSE
CHR CHR$
CHRB CHRB$
CHRW CHRW$
CINT CLNG
COS CSNG
CSTR CVAR
CVDATE CVERR

ShowD - H

DATE DATE$
DATEADD DATEDIFF
DATEPART DATESERIAL
DATEVALUE DAY
DDDB ERROR
ERROR$ EXP
FIX FORMAT
FORMAT$ FV
HEX HEX$
HOUR

ShowI - L

IIF IMESTATUS
INSTR INT
IPMT IRR
ISDATE ISEMPTY
ISERROR ISNULL
ISNUMERIC ISOBJECT
ICASE ICASE$
LEFT LEFT$
LEFTB LEFTB$
LEN LENB
LOG LTRIM
LTRIM$

ShowM - Q

MID MID$
MIDB MIDB$
MINUTE MIRR
MONTH NOW
NPER NPV
OCT OCT$
PARTITION PMT
PPMT PV
QBCOLOR

ShowR- S

RATE RGB
RIGHT RIGHT$
RIGHTB RIGHTB$
RND ROUND
RTRIM RTRIM$
SECOND SGN
SIN SLN
SPACE SPACE$
SQR STR
STR$ STRCOMP
STRCONV STRING
STRING$ SWITCH
SYD

ShowT - Z

TAN TIME
TIME$ TIMER
TIMESERIAL TIMEVALUE
TRIM TRIM$
TYPENAME UCASE
UCASE$ VAL
VARTYPE WEEKDAY
YEAR