Vista - How to embed manifest in TCL binary? - mt.exe corrupting my binary

I am trying to embed manifest in my TCL executable.
This application is an admin program and hence I would like to provide
requestedExecutionLevel=requireAdministrator in the manifest.

I am using mt.exe as following
mt.exe -manifest myapp.exe.manifest -outputresource:myapp.exe;1

Manifest gets added but the size of resulting exe drop from 1422KB to 688KB
In short file gets corrupted and cannot be run on any version of windows.

If I try same thing on a visual C++ binary it works perfectly fine.

Is mt.exe partial towards visual studio generated binaries?
How about manifesting executables created in Perl, TCL or any other launguage?