Second monitor not recognised

[disguisedrobot]

I'm having problems with dual monitors on my asus 5850. My first monitor is a DVI and the second is a VGA. The first works perfectly fine. But for my second monitor, when I use the VGA to DVI and then the the DVI to D-sub, the monitor is just blank. Windows and Catalyst Control Centre fails to recognise the second monitor is plugged in at all when I try to detect it. However, if VGA to DVI is used for the second monitor and plugged into the DVI socket of the card it works fine.

Any ideas on what this could be? Could it be a problem with the port on the VGA card? Or even the D-Sub adaptor itself?

Running Windows 7 Ultimate, Asus EAH5850, Asus P6X58D-E. First monitor is a Samsung SyncMaster 226cw and the second is a ViewSonic VX922.

 

[disguisedrobot]

Sorry, I've made a mistake. By D-Sub I mean HMDI. So it's the DVI to HMDI adaptor I could be having problems with..