SMB denied access since upgrade El Capitan

We did an upgrade of a couple of iMacs in our business environment to OSX El Capitan.

Since this upgrade, the SMB shares to network folders are not working like before. As you can see on the image some maps are blocked. This happens random and the user rights are OK! On OSX Yosemite everything worked just fine.

I tried using CIFS:// instead of SMB. But this doens't work. Maybe you guys know a solution?