System Generator. Estandard exception in FFT block
Just a guess but looking at:

'C:\My Dropbox\Archivos sobre mi PFC\Files_Matlab\System Generator\Mis pruebas\bitstream\FFTv4*/*fftv4_cw.ise'

Note that '\' used in the majority of this line is the proper windows directory separator.  The '/' used in the rest of the error and the stared bit above is not the correct directory separator for windows.  

For instance this:

'C:/My Dropbox/Archivos sobre mi PFC/Files_Matlab/System Generator/Mis pruebas/bitstream/FFTv4/sysgen/fftv4_cw.ise'

is using the forward slash which isn't the windows directory separator.

As such I would venture a guess that there is an error somewhere in your project that set the directories incorrectly which is resulting in this exception.  

It is possible that whatever library is doing this would accept either forward or backward but I doubt it, and very much doubt it would allow both versions in one path.

EDIT: Got that backwards fixed...