Q:

Why do I get the error "Unsafe code may only appear if compiling with /unsafe"? 

Why do I get the following error? 

Unsafe code may only appear if compiling with /unsafe"? 

I work in C# and Visual Studio 2008 for programming on Windows CE. 

A:

To use unsafe code blocks, the project has to be compiled with the /unsafe switch on. 
Open the properties for the project, go to the Build tab and check the Allow unsafe code checkbox. 

A:

Here is a screenshot:

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A:

Probably because you're using unsafe code. 
Are you doing something with pointers or unmanaged assemblies somewhere?