OK, now I understand. I have used your suggestion for Initialization :> to define the function and root finding and that solved my issue. Thank you again.

I really appreciate your continued help. Yes you are correct in stating that I want to find the root of 1 + a1p + a2p^2 - z == 0 when p has different values from the slider (after multiplying it by 100). I tried your suggestedcode but I still get an error:

Moreover, a slider of 'guess' for the cdf file will not be an attractive option to the end user.

I decided to modify my function definition to remove the requirement of multiplying slider value of p by 100. I am struggling to understand why my revised and much simplified code for root finding still gives an error:

Remove["Global`*"];
A1 = .3265;
A2 = -1.07;
Manipulate[
 Module[{func, z},
  func[z_] := 1. + A1*p1 + A2*p1^2 - z;
  Evaluate[z /. FindRoot[{func[z] == 0}, {z, 1}]]
  ],
 {{p1, 10, P }, 10, 40, Appearance -> "Labeled"}
 ]

In my attempt to solve the bigger problem, I am still having some issues with Manipulate and FindRoot. I have used your suggestions above.I think I am close but I need some helping hand.

Here is another simplified version of my problem definition:

Remove["Global`*"];
A1 = .3265;
A2 = -1.07;
Manipulate[
 Module[{func, z},
  func[z_, zp_] := 1. + A1*zp + A2*zp^2 - z;
  Evaluate[(2. + z0) /.

    {z0 -> 
      Evaluate[
       z /. FindRoot[{func[z, zp] == 0} /. {zp -> p1*100}, {z, 1}]]
     }]
  ],
 {{p1, 10, "P"}, 10, 20, 1, Appearance -> "Labeled", 
  ImageSize -> Small}
 ]

My objective is to solve a nonlinear equation 'func' that has a variable zp that needs to be manipulated by slider. The root of this equation 'func = 0' then gets used in the target variable '(2. + z0)' that I need to output within the Manipulate.

I am getting some errors related to the FindRoot as shown below. I would really appreciate some suggestion to modify the code to resolve these errors.

You are making things too complicated.

Manipulate[
 eq = 1 + a*x + 2 x^2 - 1/x;
 x /. FindRoot[eq == 0, {x, 1}],
 {{a, 10, "a"}, 0, 20, .1, Appearance -> "Labeled", ImageSize -> Small}
 ]

or you can put everything inside Module to limit scope of symbols used inside the function

Manipulate[
 Module[{eq, x},
  eq = 1 + a*x + 2 x^2 - 1/x;
  x /. FindRoot[eq == 0, {x, 1}]
  ],
 {{a, 10, "a"}, 0, 20, .1, Appearance -> "Labeled", ImageSize -> Small}
 ]

Add the option

SaveDefinitions->True

To your Manipulate finction. Alternatively you can add your function definition ti an Initialization option of your Manipulate.