weird problem with skin and masterpage with inline code

[kelmen]

Greeting,

I have a weird problem. Working fine before I incoporating theme and
skin.

my sample is an aspx file using masterpage. working fine.

then when I incoporating theme and skin, keep getting error:

The Controls collection cannot be modified because the control contains
code blocks (i.e. <% ... %>).

after many trial, the error resolved if I:

at masterpage, I have a client script with inline coding to refering
the main form:

<script language="javascript" type="text/javascript">
var m_frmMain = null;

function OnFormLoad()
{
m_frmMain = document.<%=frmMain.ClientID%>;
}
</script>


if I change or disable the inline code say to : m_frmMain =
document.forms[0];

it worked fine then!!!!

Something wrong or incompatible between the theme and masterpage inline
coding?