RFC_ERROR_SYSTEM_FAILURE error when connecting to BEx

I get the following error message when I try to connect to BEx Analyzer 3.5 in Excel 2010:

Error Group

RFC_ERROR_SYSTEM_FAILURE

Message

Error when opening an RFC connection (>>>invalid RFC handle<<<<).

I have no problems connecting to BW backend.  It's only BEx Analyzer that gives me this error.  I tried to use transaction rrmx, but I get the same error.

What could be causing this error?  I've never had these issues before.  I started getting the error today.  I rebooted my computer, but that didn't help.

Thank you for your help.

Nadia