Unrecognized image file format - UiBinder

I'm getting this error when I put

<ui:with field='res' type='com.mycomp.mygwt.client.Resources'/>

In my UiBinder file where the error is:

    [DEBUG] [MyGWT] - Rebinding com.mycomp.mygwt.client.Resources

    [DEBUG] [MyGWT] - Invoking generator com.google.gwt.resources.rebind.context.InlineClientBundleGenerator

    [DEBUG] [MyGWT] - Preparing method logo

    [TRACE] [MyGWT] - Adding image 'com.mycomp.mygwt.client.Resources.logo'

    [ERROR] [MyGWT] - Unrecognized image file format

    [ERROR] [MyGWT] - Generator 'com.google.gwt.resources.rebind.context.InlineClientBundleGenerator' threw an exception while rebinding 'com.mycomp.mygwt.client.Resources'

The image file in the path is a PNG file which I use in my previous GWT application. I really don't know why GWT is throwing the error.

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