network password not recognized on new server

I had to replace a server in a windows 7 workgroup. The server is named the same and the password is the same but I keep getting wrong password issues with old work statoins. New stations can log in fine.

If the Windows Server is not a domain controller (Windows AD Domain) there is no central repository for user authentication.
And in a workgroup environment in order for client machines / users to access shares on the "SERVER" they will have to have a username and password on the "SERVER" that is the same as the one they are using to log on locally to their machines in order for passthrough authentication to work. Otherwise they will be prompted for credentials at which point they can check the box to remember the credentials and they will be preserved in the credentials vault. If anything has changed regarding those credentials you may need to delete and re-establish them. Also double check and confirm that the WORKGROUP name is the same on all computers and server involved.
Same deal if you are using a Windows 7 machine as a "SERVER".
In an active directory domain situation the machine SID is part of the authentication process so the machine must have a computer account in the domain as well as the user must have a user account in the domain.

solved with a ipconfig /flushdns and then reboot

Good job, glad to hear that you managed to resolve your problem.
Although I am not sure how or what DNS might have had to do with the actual problem, since typically workgroup environments aren't often using DNS locally to resolve anything and normally do not even have a DNS server present on their subnet but more likely a DNS forwarder (typically the router). Normally workgroups rely on WINS or more often NetBIOS to resolve netBIOS names (computer friendly names) to IP Addresses. DNS is used solely to resolve FQDNs (Fully Qualified Domain Names) to IP Addresses and I wouldn't suspect that in a workgroup environment you have any FQDNs that need resolving.
Anyhow..... great you have it sorted out now.
Regards
Randy