"Unknown" and "Invalid use of Null" errors when performing SQL queries

"Unknown" and "Invalid use of Null" errors when performing SQL queries

A customer of ours has encountered some strange behavior. Our software
uses a database and we connect to it by the JET engine 4.0. We retrieve
information by using SQL statements. So these commands are the same for
every installation/user. We have a lot of customers but there is only one
who encounters the following issue:
Some SQL statements cause strange errors:
SELECT * FROM Dimensions
=> Successful
SELECT * FROM Sections where true=false
=> Error : "Unknown"
SELECT Alpha, Ys, Zs FROM SectionProperties WHERE Id = 1
=> Error : "Invalid use of Null"
These statements run without a problem on any other machine.