c# - Clicking a button in the webbroswer -

i know how change values have done many times on several programs, confused on error continue get...

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an unhandled exception of type 'system.nullreferenceexception' occurred in destiny redbull code generator rage.exe

additional information: object reference not set instance of object.

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the code causing error follows...

htmlelement lenseq = doc.getelementbyid("lenseq"); 

the entire code is...

private void form1_load(object sender, eventargs e)     {         {             htmldocument doc = webbrowser1.document;              htmlelement lenseq = doc.getelementbyid("lenseq");             lenseq.setattribute("value", "7".tostring());              htmlelement letters = doc.getelementbyid("letters");             letters.setattribute("value", "abcd".tostring());         }          {             htmldocument doc = webbrowser1.document;             htmlelement submit = doc.getelementbyid("click generate letter sequences");             submit.invokemember("click");         }     }