Mac Pro won't connect to iMac's shared folders

Hi,

I have an iMac with some shared external HDDs that I use to store data.
I could see my iMac and all i'ts shared discs from my Mac Pro's Finder but since I updated my iMac to Sierra I can't connect to it anymore. I have not changed anything at all in the user accounts or the shared devices.
I can see it in the shared list of my Mac Pro's Finder but when I try to connect it says "no connection"
I use the ethernet to connect both and a ping to the iMac's IP gives a possitive response.

Is there sonthing I am missing about Sierra?

Thanks in advance

It may be that you need to change the security of your network. Sierra seems to have done away with older protocols and requires WPA2+AES.

But I do see it and read files with my iPad 3 from those shared devices via WiFi

An iPad 3 does not use the latest operating system and is capable of handling older security protocols, so switching your iMac to Sierra hasn't affected the iPad's ability to communicate with the MacPro.

Is this an early Mac Pro running Snow Leopard?

The iMac is a late 2012 with Sierra.. The Mac Pro is an early 2009 with el Capitan.
But the only problem appears when I try to connect the Mac Pro to the iMac's shared folders.

Silly question...File Sharing turned on in System Preferences?

File sharing is on and all users have the their priviliges as they were before upgrading to Sierra.

Maybe, when you upgraded to Sierra, the permissions were changed and you just need to turn off and back on the File Sharing, and/or their privileges? Can you compare each setting on both machines at the same time?

Ok, I think it's solved now. Checked users, permissions, energy settings and now it seems to work fine.
We'll see.

Thanks a lot for your support