Hi John,
You are using win 10 , aren't you ? if yes, I recommend you to upgrade your SAP B1 version. The latest patch release is SAP B1 9.1 PL12.
To avoid this issue repeats, you must upgrade it.
Although your server and your other PC clients work wells, you must still upgrade it to avoid other issues in your SAP B1 current patch release.
Rgds,
Jimmy