Hi fuddyduddy,
I'd also check the version of SMB that your NAS is using - I had comparable problems in the past that I traced to this. The 'official' v0.3 build is quite fussy, and needs to be able to use SMB1 in order to work correctly. Janui & Gearhead's v.05 beta is more forgiving of recent SMB versions.
You mention that your NAS is a Synology model. The relevant settings in Synology DSM are as follows:
Control Panel > File Services > SMB/AFP/NFS > SMB: 'Advanced' button > set 'Maximum SMB protocol' to SMB3, and 'Minimum SMB protocol' to either SMB1 if you're still on the official Rune v0.3 or SMB2 if you're on v0.5 beta.
I hope this helps.
Peace and friendship,
englishtim