Converting to coded step removes(?) System assembly

Hello,

I converted a step to a coded step in my test file 'Policy_Coverage'.  When attempting to execute, I receive the errors below, all of which are in a different test file 'GL_Smoke_Driver'.  The execution worked fine before I converted to code, and when I remove the Policy_Coverage.cs file, execution is normal again.  I double checked the assemblies and they are all there.  What the heck happened?

j:\...\GL_Smoke_Driver.tstest.cs: Line 9: (CS0234) The type or namespace name 'Data' does not exist in the namespace 'System' (are you missing an assembly reference?)
j:\...\GL_Smoke_Driver.tstest.cs: Line 11: (CS0234) The type or namespace name 'Xml' does not exist in the namespace 'System' (are you missing an assembly reference?)
j:\...\GL_Smoke_Driver.tstest.cs: Line 78: (CS0246) The type or namespace name 'SqlConnection' could not be found (are you missing a using directive or an assembly reference?)

Many thanks,
Alan