Looks like the act of MBAM opening the file to scan it has triggered a File System Shield scan, if you check the avastUI, Real-Time Shields, File System Shield, it should show the last file infected (if you haven't rebooted).
That should give the location also, what was that ?
Did you send it to the avast chest ?
The strange thing as I mentioned is that avast didn't detect it in the VT scan. However that is showing a previous scan from December 9th, which in virus terms is a long time so it probably said this has been scanned before.
If it does it is always best to have it scan the file again.
I have that file and I have scanned my copy RTCOMDLL.dll MD5: C650FF877B54943F99826F4100F61CA9 file size 256 KB (262,144 bytes) 19 November 2007, 09:12:58. So I don't know if this is the same as yours (doesn't appear so as the two VT scans yours and mine have different MD5s) ?
VT results for my RTCONDLL.DLL 0 detections, the same as my avast scan, image1. Ensure that you have the latest avast virus signatures and scan it again.