Do you know how to solve this?
There is really no solution.
You basically have a client / server relationship between the machine hosting the shares and the other one needing the shares.
If this share host (server) is not available when the client comes on line requesting the shares then the client machine is out of luck.
I suppose if you're patient enough, over time the NetBIOS information will propagate between the machines and the client machine might regain access.
The best solution (such as it is) is to make sure that the server machine is always on line or at the very least is booted before the client.