Okey... It seems that I've solved this problem...
I found that I read the documentation not carefully. There is such text in that tutorial:
"Select the Open as Main Project check box and the Open Required Projects check box."
But I've missed the second step. The "required project" has all I need... it has the toplink-essentials.jar and with that project and that library all compiled well. It strange that the direct inclusion of toplink-essentials.jar in my main project didn't help.... but I assume that there may be other important stuff in the "required project"...
Thanks everyone.
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