Hi Antoine,
Would you please provide the exact details of ESX and vCenter versions which is being used?
In addition to that, please send us the logs by following this:
1. Restart IOInsight VM (so that older logs will be cleared)
2. Reproduce the login issue
3. Download logs from the link in IOInsight web interface
4. email logs to ioinsight@vmware.com
We'll look into this issue. Thank you!
Regards,
Midhun