NullPointerException in process with GSP

Hi,

I'm using RapidMiner 5.1.014 and tried to create a process including Generalized Sequential Patterns. I'm using a very simple test source containing examples of the following form: I retrieve the data, use the Nominal2Binominal operator on the column item and then feed this into the GSP operator. In the GSP operator, I set "customer id" to my attribute "Customer" and "time attribute" to my attribute "Time". When running this process, I get a message that my process failed and the log contains:

[tt]Jan 9, 2012 5:50:11 PM SEVERE: Here:          Process[1] (Process)
          subprocess 'Main Process'
            +- Retrieve[1] (Retrieve)
            +- Nominal to Binominal[1] (Nominal to Binominal)
      ==>  +- GSP[1] (Generalized Sequential Patterns)
Jan 9, 2012 5:50:11 PM SEVERE: java.lang.NullPointerException[/tt]

Did anyone run into similar problems and can provide a solution? I searched the forum and internet, but couldn't find any pointers for what I'm doing wrong.

Thanks a lot,
Conny