The program uses an eval statement and is compiled with fast mode turned off.
When fast mode is turned off, the eval statement allows new variables to be declared at runtime with local scope. These new variables can shadow the global variables, which makes any reference to a variable not explicitly defined in the local scope potentially ambiguous.
To correct this error
Compile with the fast option on.
Avoid using the eval statement.
Use only the variables available in the current local scope.