BCC Drop shadow on source with alpha channel (like a title) don't work at all with Media Composer 8.5.3.  I used this plug-in a lot in Avid DS, but with Media Composer, not work at all !

Have you tried promoting the simple matte key clip to 3D, then using its own shadow effect? No need to go to BCC at all.

I know that, but I need a soft drop shadow.

If you're making the titles with the Title tool, then SHIFT+CONTROL+H will give you controlable soft shadow.

But my titles and idents are coming with alpha channel from infographists who delivered to me all titles.  Sometime, the clients want a soft shadow over idents and I want a fast solution to give them this soft shadow without to go back and forth to infographists.  The solution normally I use, I take the BCC drop shadow and that, it !!  But for now, this plug-in don't wotk at all !

What version of BCC?  
FWIW With regular usage up until MC 7 and BCC 8 I have never had an issue with BCC Soft shadow on PC's. (I have not tried MC 8. + with BCC)