Thank you to 'davidgal' and 'DomH' for their quick answers
First of all, I apologize for my poor english, english is not my native language and I hope you will understand my message and my explanations.
I found the problem. My username (Hervé) contains an 'e acute'.
XyGrib configuration is written in file "C:\Users\Hervé\AppData\Local\openGribs\XyGrib\xyrib.ini".
This file contains a parameter "appDataDir=C:/Users/Herv\xe9/AppData/Roaming/openGribs/XyGrib" which defines where XyGrib data are store.
In order to try to fix the prolem, I decided to move XyGrib data to another directory which does not contains 'e acute' in the path, for exemple "E:/Chart/openGribs/XyGrib".
To do that I have copied data from previous directory to new directory.
Then with 'regedit' program, I have modified the key "HKEY_CURRENT_USER\Software\xyGrib\OrganizationDefaults\main\appDataDir" to the new value "E:/Chart/openGribs/XyGrib".
And now it works perfectly. After running XyGrib the file "C:\Users\Hervé\AppData\Local\openGribs\XyGrib\xyrib.ini" is updated with the new configuration.
I dont know where is the reference: in the register file or in the 'xygrib.ini' file ?
Conclusion: do'nt use accents in your username. As i am retired and if I have some time I will try to have a look at the source code (during my working life, I wrote a lot of programs in Fortran, C, C++, java, javascript, shell, ....).
I join a screen copy of the register file and a screen copy of XyGrib.
Thank you for your answers
Best regards,
Zebulon31