Yes you can disable the shields of Avast, however you cannot disable Avast while having another AV (Avira) in your machine and expect your machine to work properly.
Since you continue to have problems, I suggest that you perform a mini-dump for Avast to analyze:
Here is additional information on how to invoke a memory dump file: http://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=71.
Please, zip and upload the C:\Windows\Memory.dmp file to this anonymous ftp server and name it uniquely: ftp.avast.com/incoming. Avast will analyze it and respond back to you in this thread or to your email. Thank you.