Syed,
I am not sure what you mean by "Main processor is working with different resolution LCD modules.(320x240), (800x480), (640x480), (1024x768)" ?
The THS8200 MUST be configured in a mode which corresponds exactly with the output that your processor is generating.
The THS8200 does not do scaling.
Of the resolutions you mention above 320x240 is not a VESA compliant resolution I don't think and you will not be able to drive this resolution directly to an analog monitor.
When you change the processor output resolution it is necessary to change the THS8200 configuration to the same resolution/configuration. Is this what you are doing?
Please make sure that the processor output timing is compliant with the VESA specification for the specific mode used.
BR,
Steve