I try to setup Avast Premier to let me send files through bluetooth from my mobile phone to a PC. Both have Avast, the PC is a Windows 8.1 Update 1 machine, and I could transfer files when I disable Avast on the Windows machine. I could not find a setting for the bluetooth at all. I find Avast very difficult to find where to setup things also.
I had same issues then I looked up were Bluetooth system files area add to add them which it worked for me. Here is the instructions
Open Avast
Click menu on top right
Then click settings
Then in middle left side part find " Blocked & Allowed APPs"
Next Click on Allow APP
Next bottom Click on " Select APP Manually"
I added these two you add one at a time both in the System32 folder
C:\windows\system32