This usually means the eConnect service account user needs to have its regional settings changed to English/US settings. Specifically, the decimal separator setting changed to periods instead of commas.
1. Logon onto to the Windows machine as the eConnect user.
2. Change the regional settings for that user to English US (Anglais Etas-Unis)
3. Restart the eConnect service
4. Log off and log back on as the GP user
Here are some links with instructions: