There was an error in an expression in encryption at Output Expressions : Neither variable(s) nor rule(s) found: expression

We need to see the code of that expression.

if(
  or(
    a!isNullOrEmpty(ri!message),
    a!isNullOrEmpty(ri!key)
  ),
  null,
  a!localVariables(
    local!message: char(code(ri!message)),
    local!max: 16,
    local!splitted: a!forEach(
      items: enumerate(
        ceiling(length(local!message) / local!max)
      ),
      expression: a!forEach(
        items: fv!item * local!max + 1 + enumerate(local!max),
        expression: index(local!message, fv!item, {})
      )
    ),
    a!forEach(
      items: local!splitted,
      expression: rule!ALM_Encryption(message: joinarray(fv!item), key: ri!key)
    )
  )
)

if(
  or(
    a!isNullOrEmpty(ri!message),
    a!isNullOrEmpty(ri!key)
  ),
  null,
  a!localVariables(
    local!message: char(code(ri!message)),
    local!max: 16,
    local!splitted: a!forEach(
      items: enumerate(
        ceiling(length(local!message) / local!max)
      ),
      expression: a!forEach(
        items: fv!item * local!max + 1 + enumerate(local!max),
        expression: index(local!message, fv!item, {})
      )
    ),
    a!forEach(
      items: local!splitted,
      expression: rule!ALM_Encryption(message: joinarray(fv!item), key: ri!key)
    )
  )
)

And "ALM_Encryption"?

its a aes-128 implementation and is lengthy. I have used the rule in interface and is working fine. Other rules are working fine in process model.

My guess is that there is a duplicate parameter keyword somewhere. Like

expression: expression: append(.....)

This is not caught by the syntax checker.