VB6 risks and Migrating

I'm wondering if anyone can help me. My Company is in the process of making the decision of migrating an existing application written in VB6 to .Net. I am presenting a list of risks around keeping VB6 to help make their decision in switching to .net. Risks around VB6 include the following:

• Decreased functionality
• Security Risks
• Performance Lag
• User Interface issues
• Limited technical support
• Incompatibility issues

With regards to security I have been asked to expand on this. The application is internal and won't be exposed to customer. With this in mind it will sit behind the company security infrastructure so will this decrease the issue of security. Also are there any more risks apart from the above which I have not considered

thanks