Why won’t MacBook Pro recognize Kingston USB thumb?

My MacBook Pro 15' no longer reads my 16GB Kingston USB.
A few weeks ago, it still worked perfect.
Attempting to plug my USB in either USB Ports there appears a notice saying
"The disk you inserted was not readable by this computer."
Three options are given:
"Initialize..." "Ignore" and "Eject"

How can i solve this problem?

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