Found the solution to the problem.
I've just reinstalled avast! and it happened again, no access! So the probem had to do with avast! or, most probably, problems in the system caused by the avast! installation.
The complete error message was:
"\\192.168.12.84\share is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access permissions.
Not enough server storage is available to process this command."
The last line I din't post it before and it should be the best clue to solving the problem.
So, after investigating the problem a little bit, I finally found this site (
http://www.pcdoctor-guide.com/wordpress/?p=174) with the soultion:
Navigate to the following registry key HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services
\LanmanServer\Parameters
and modify create the variable IRPStackSize=50
50 (decimal, 0x32 Hex) may be exagerated which is the max val, but after a reboot it did work.
Thanks, I hope this info helps someone...