[URgent] Management console screen freeze with Windows 2008 R2 server

Dear Sir,

We've installed the serv-u latest version15.0.0. and everything runs well on platform Windows 2008 R2 server for last 12 months.

Lately, we noticed that Ser-U management console is freeze at below screen when every time i simply click on "management console"

Please advise how I can solve this problem?

Image may be NSFW.
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Ricky