Converting Textbox Txt to int?

I'm trying to convert text from a textbox to an int, which is then used as a parameter when calling a method from a webservice. I'm getting this error:

An exception of type 'System.FormatException' occurred in mscorlib.dll but was not handled in user code

Any help?

Heres my code

            int amount= int.Parse(txtAmount.Text);

            Service1Client connectionToService = new Service1Client();

            lblResult.Text = connectionToService.getCurrencyName(amount, "Rupee", "Euro");