unable to connect to shared drives [intermittent issue]

[frazzle]

past few weeks iv been having users that use fortinet to connect to an internal network. in the past they would connect to our network via vpn and then access there sharedrives. But recently (and this has been happening more frequently). users have been unable to establish a connection to there share drives even though they are on vpn. There was not sudden updates that or changes and these users arent isolated to one area. Is there a way to reset the settings or clear maybe some cache stored somewhere, because the machine isnt pointing to the network shares. What i have noticed is once connected, the bytes received are much lower than the bytes sent out. After disconnecting and reconnecting a few times. Sometimes the received bytes increases and the drives are able to be seen. 

[SJFriedl]

Check that you have DNS connectivity to the inside network, perhaps by pinging some known hostname: if it doesn't look up the hostname, it's a DNS thing.

[frazzle]

when i ping a share by the IP address i get no response. But its odd that after i disconnect and reconnect a few times. eventually its able to connect. I have tried in the past to flush the DNS to see if that could help. But i have noticed when the traffic coming in is significantly lower then whats going out (based off the information from fortinet client) Then the drives wont connect and my network isnt identified on the lower task bar. Is there a way to clear old information that may be stored somewhere in a fortient file that can reset old information maybe?