.Net application not getting Pen clicks on tablet

I have C#/.NET 3.5 application that runs on Win7 Tablet. Tablet is dual core, with attached Pen. There are issues with getting click events from Pen in app.

I attached additional USB mouse.

1) When I start PaitBrush, clicks and drags by both Mouse and Pen behave the same, all clicks work, drags work, performance is fine

2) when I start my C# application, and click from Mouse lunch events and it works reliably ( tho a bit slow, compared to desktop)

3) when I start my C# application, clicks from Pen are IGNORED, or worked sporadically. Looks like maybe one in 10 clicks is received by C# app.

Processor time is all time <10%. Tablet has 2GB, and usage goes to about 600MB.

Why clicks from Pen do not work in .NET/C# app, and work in Paintbrush?