query expression compile error

[DennisD]

I have the query expression below where the [Eqnum] field is contained in a
linked SQL table

InStr(1,[Eqnum],"-")

ordinary queries work fine; this one and others similar using MID or LEN
give the same result

Compile error. in query expression 'InStr(1,[Eqnum],"-")'

It only seems to have happened after I converted from Access 97 to Access
2003. How can I get these queries to work? Help!