Damp Patches on Casement Frames

[mypyrex]

The exterior of my double glazed windows is PVC but the interior is wood. I have recently noticed evidence of dampness on the lower sections of the woodwork such as around the corner joints. This appears on both the opening and the fixed casements. Anyone know what the problem might be?

[thedoctor]

Water is obvioulsy getting in from outside somewhere and you must establish where this is. Look for cracks in sealant or bricks etc.