I suggest that you read this to help your understanding of scope.
I can't give a specific answer, because that would require me to look into the design of your report.
But, based on the error message, it seems that the expression is being evaluated at a point in the report where the Text58 field is not defined or invalid.
As an aside, it is good practice to give your controls meaningful names: 'Text58' means nothing and is difficult to maintain.
If you haven't even tried to resolve your issue, please don't expect the hard-working volunteers here to waste their time providing links to answers which you could easily have found yourself.