Application works only as administrator

What exactly is your application doing, is it trying to read data from some path? UAC will protect certain paths and you'll see the 'Access is Denied' message

Have a look at the call stack....where is the error occurring. Is it trying to read \ write data?

This thread on MSDN[^] shows some possible solutions

Without knowing what your application does, it is impossible to give an accurate answer.

The problem is certainly related to permissions in some way but exactly how is not ascertainable from your question.

Does the application try to write to the Program Files Folder?
Does it try to modify the Registry?

What does it do?

The most common problem that causes this is writing data to a folder under Program Files. With Vista and Windows 7, program Files is now ReadOnly to normal users to protect application code files.

The solution is quite simple. Write your data to a folder that is more appropriate. Program Files should never be used to store program data.

Which folder is appropriate depends on what this data is for and who needs it. Is it going to be shared among all users on the machine or is it different data for each user? Is it going to be portable, meaning should it only be on that one machine, or should the data follow the users profile from machine to machine (IF and only if the environment supports roaming profiles!)?

Look at the documentation for Environment.GetFolderPath for how to get the path to various folder locations. Look at the documentation on enumeration members for SpecialFolders for descriptions of what each of these folders is meant for.