c#, asp.net - nullreferenceexception - vigilant anxiety set an instance an object

definition variables use:

guid fldproid = (guid)ffdpro.getproperty("fieldid");
string fldprovalue = (string)ffdpro.getproperty("fieldvalue");
formfielddef fmproflddef = new formfielddef();
fmproflddef.key = fldproid;
fmproflddef.retrieve();
string fldproname = (string)fmproflddef.getproperty("fieldname");
string fldprotype = (string)fmproflddef.getproperty("fieldtype");

lines giving problem (specifically line 4 (htxtbox.text = ...)):

if (fldprotype.tolower() == "textbox")
{
    tag htxtbox = (label)findcontrol(fldproname);
    htxtbox.text = fldprovalue;
}

all information collected database correctly, however tag goes screwy. any ideas?