Last week I needed to reset a BPOS account password for a new user that I was setting up. I logged into the BPOS control panel and reset the users password, copied the new one to the clipboard and then proceeded to try and login as the user through the web interface. The web interface took the new password and as expected it then prompted me to change the password as this was the first time of logging on as the user. However on entering a new password I got "server is busy or you’ve lost your internet connection". I obviously haven’t lost my internet connection and I am hoping that the Microsoft servers are not that busy.
Attempting to login through the single sign on client gave me the following error message – ”Your password could not be changed due since we couldn’t connect to the service. Please check your network connection or contact your service administrator”.
I couldn’t find anything useful online for this issue so I logged a ticket with BPOS support. They came back with a powershell script (below) that fixed the issue and admitted that this is a known problem that sometimes occurs when a password is changed in the gui.
First the BPOS migration tool needs to be downloaded on a machine with powershell installed. Although the migration tools themselves are not required for this particular issue, it provides the extensions to powershell to allow you to manage BPOS. If you are managing BPOS users then you should have this installed already. If not, the migration tools can be downloaded from either the 32bit migration tool (transporter tool) or the 64bit migration tool pages.
Once installed, from the migration tool powershell prompt, enter the following
$tcred=Get-Credential
Note: In the Credential Popup Window, type in the Exchange Online Administrator account & password.
Once it is saved, type in the following command. I’m not sure that this first step is needed as you are prompted for the credentials again when you enter the next line, but as Microsoft said it, it must be true 
The second command resets the user password –
Set-MSOnlineUserPassword -identity emailalias@bposemaildomain.com –Password strongpasswordhere -ChangePasswordOnNextLogon $True
You will then be able to login as the user with the new password provided above. Note you will be prompted to change the password again, but this time the password change should be accepted.