document.getelementbyid(...) is null or not an object

Greetings,

i have an html button with id=button1 and name = button1

i make the following script in the head tag

<script language ="javascript">
document.getelementbyid('button1').disabled=false;
</script>

but when i run the page i get the following javascript error:

document.getelementbyid(...) is null or not an object

your help is highly appreciated
 
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