It looks like your license (available seat) is already taken by another computer. We usually recommend to have as many "seats" as number of concurrent users that'll work with scenes containing Forest object(s). The license is not assigned by opening 3ds max or any scene which doesn't include any Forest object. Once anyone opens a scene with some Forest object(s), the license is automatically assigned to that computer. The license handling process is fully automatic - the license is sent when needed and released to the "free & available" status when not in use - that happens shortly after closing the 3ds Max (within seconds) / scene with Forest objects (within minutes).
You can double check that under the Computers
tab of the Itoo Software License Manager. There is an informative list, that shows actual computer(s) data (Hostname, IP address, Start Time, Product) with license assigned (borrowed from the license pool) and "in use".
Please feel free to send us the log file from the Itoo Software License Manager
- License Server
tab - View Log...
to analyse it here. Thanks in advance.
"... can one computer with windows 10 work with FP (distribute vray render) while the other computer is windows 7?"
Well, the only restriction is to use on all your render nodes the same release of Forest Pack. The OS version shouldn't bring incompatibility issues, but that'll depend also on 3ds max & renderer versions. Generally, it's recommendable to install same versions of any software to prevent incompatibility issues.