The formula refers to a UDF or UDT of the wrong object type

Explanation of error:

This formula includes a reference to a user-defined field or user-defined table, but the project contains more than one user-defined field or user-defined table of that name of different types and the formula cannot evaluate the reference to one of the types of user-defined field.

Example:

Cost/(UDF("Value1")*(UDF("Value2"))

The example above would result in this error if the project contained two user-defined fields called Value1, one of which was numeric and defined against tasks and the other of which was a date and defined against milestones, if the formula was evaluated against milestones.

How to resolve this error:

Rename any user-defined fields or user-defined tables in the project whose names are not unique.