Folder connection fails when using alternate credentials in Power Query

[Anonymous]

We're facing an issue with using a folder query on a network share. The network share in on a non-domain joined server, and we're using a local service account. Mapping the network folder in Windows works fine from both developer machines and the gateway server. Additionally, when connecting in Power BI Desktop using my (domain) credentials, connecting and refreshing works fine. However, when changing to alternate credentials and attempting to connect to the share, we get the following error:

Similarly, when attempting to use the connection on the gateway, we get the following error:

We saw initially that traffic was blocked on our network, but have since opened ports 139 and 445. Are there other ports that should be open? Any other steps that we may have missed? 

Regards,

Tore