According to CNET Specs on the AMD Radeon HD 6450 with 1/2 gbyte of vRAM, the maximum Monitors it supports is 2: AMD Radeon HD 6450 - graphics card - Radeon HD 6450 - 512 MB Specs - CNET
But the Sapphire Radeon HD 6450 with 1 gbyte of vRAM also mentions that it only supports a maximum of 2 Monitors: AMD Radeon HD 6450 - graphics card - Radeon HD 6450 - 512 MB Specs - CNET
Probably you can't have both VGA and DVI-I connected at the same time.
I think the card you are referencing here only has TWO physical outputs and a VGA adapter as shown in the pic on the webpage you referenced.
I am talking about the HD6450 that has THREE physical outputs, VGA, DVI, and DisplayPort, as shown, for example, here: