Business objects formula fields not accesible to edit

Summary:

Hi all, I would appreciate any help with the following.

I am trying to setup a formula field in a BO.

The text for the formula is as following:

=lastNumber_2 = lastNumber+''

if (length(lastNumber_2) == 5) {countryCode+companyCode+(lastNumber+1)} 

else if (length(lastNumber_2) == 4) { countryCode+companyCode+'0'+(lastNumber+1)} 

else if (length(lastNumber_2) == 3) { countryCode+companyCode+'00'+(lastNumber+1)} 

else if (length(lastNumber_2) == 2) { countryCode+companyCode+'000'+(lastNumber+1)} 

else if (length(lastNumber_2) == 1) { countryCode+companyCode+'0000'+(lastNumber+1)}

else { 'NA'}

My issue is that I cannot edit/access the code, as shown:

I cannot find the edit button.

Is it a bug? Am I doing something wrong?