Process failed - X-means clustering

Hi everyone,

I´m trying to execute a X-means clustering process to a range of texts included in an Excel file, but it is not possible because everytime I try it, I obtain the same fail: 

"Process Failed
The setup does not seem to contain any obvious errors, but you should check the log messages or activate the debug mode in the settings dialog in order to get more information about this problem."

The log messages are:

Jun 28, 2017 6:32:59 PM SEVERE: Process failed: operator cannot be executed. Check the log messages...

Jun 28, 2017 6:32:59 PM SEVERE: Here: 

Jun 28, 2017 6:32:59 PM SEVERE:           Process[1] (Process)

Jun 28, 2017 6:32:59 PM SEVERE:            subprocess 'Main Process'

Jun 28, 2017 6:32:59 PM SEVERE:              +- Read Excel[1] (Read Excel)

Jun 28, 2017 6:32:59 PM SEVERE:              +- Process Documents from Data[1] (Process Documents from Data)

Jun 28, 2017 6:32:59 PM SEVERE:            subprocess 'Vector Creation'

Jun 28, 2017 6:32:59 PM SEVERE:              |     +- Tokenize[2096] (Tokenize)

Jun 28, 2017 6:32:59 PM SEVERE:              |     +- Transform Cases[2096] (Transform Cases)

Jun 28, 2017 6:32:59 PM SEVERE:              |     +- Filter Stopwords (English)[2096] (Filter Stopwords (English))

Jun 28, 2017 6:32:59 PM SEVERE:              |     +- Stem (Snowball)[2096] (Stem (Snowball))

Jun 28, 2017 6:32:59 PM SEVERE:        ==>   +- X-Means[1] (X-Means)

Jun 28, 2017 6:32:59 PM SEVERE: java.lang.ArrayIndexOutOfBoundsException

The structure of the process is in the attached image. If I try the same process only changing X-means box by a K-means box, the process is working without problems and I´m obtaining the results of the corresponding clustering. 
I have also tried to do the X-Means clustering with other data input (direct input from a folder containing pdf files) and the process is not working either.

Could anyone help me?

I really appreciate your help!

Thank you very much
Alberto