err adding sandbox webpart

Question

i have sandbox user code service running in MMC and in CA as well. It gets deployed from vs 2010 without any errors.Still when I try to add a sandboxed web part I get error message like " The sandboxed code execution request was refused because the Sandboxed Code Host Service was too busy to handle the request."

I am using windows 7 proffessional OS and sharepoint 2010 rtm version.

please help me to resolve this.