You don't mention what version of mojoPortal or whether you are using the pre-compiled deployment package or source code or a build you made yourself from source code, you also don't mention which database. If using SQLite you need to check the box "Enable 32 bit appications in the advanced properties of the App pool.
Make sure you are using an IIS application pool configured for Integrated Pipeline Mode not Classic.
Make sure you have configured file system permissions correctly so that NETWORK SERVICE and IUser have read access to the full web folder and full control on the /Data folder beneath the root of the web.
Is you Windows 7 machine part of a domain? If so its possible that medium trust is being enforced ont eh IIS by group policy.
Hope it helps,