Cleaning a PDA screen

Hi

I have an IPAQ onto which was attached a screen protector.

Over time I wasn't able to press any icons/sliders etc that were at the edges of the screen so I removed the screen protector which cured the problem.

However I have another problem - A glue like substance on the screen. I cannot scrape it off as this may damage the screen and I've tried a cleaning solution but that won't shift it either.
Has anyone got any suggestions as to get rid of the glue?
Thanks

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