Pattern analysis can never be satisfied, however the rule is logically correct

When I launch the analysis of a rule I get the following message:

Pattern, name: TrafficoEntrata in Rule 'backToNormal' can never be satisfied.
Pattern, name: StatoRete in Rule 'backToNormal' can never be satisfied.

The Rule "backToNormal" is the following:

rule "backToNormal"
dialect "mvel"
when
exists Attacco( )
attack : Attacco( )
StatoRete( numero_utenti > "25" && < "80" )
TrafficoEntrata( banda_occupata > "20" && < "80" )
then
retract( attack );
end

The integer values are taken from an enumeration. Altering the conditions in this way:
numero_utenti >"25", numero_utenti < "80"
makes no difference at analysis time.

– EDIT –
how to get this error (in the simplest case)
1. create a new package
2. create a new model
2.1 in the model, create a new fact (call it Fact1)
2.2 in Fact1, add just one integer field (call it value)
3. save changes and create a new rule
WHEN Fact1( element : value > "10" && < "20" ) THEN [...]
4. save changes and try to analyse the package containing this rule

Note: these steps are all made in guvnor