Subassemblies are not backwards compatible. If you want to use something in Civil 3D 2012 and/or SAC 2012 then it needs to be originally designed in SAC 2012.
Kati Mercier, P.E.
Co-author of "Mastering AutoCAD Civil 3D 2013"
AutoCAD Civil 3D 2013 Certified Professional and AutoCAD 2013 Certified Professional
AU2012 Speaker::: CI3001: Reverse Engineering with Subassembly Composer for AutoCAD Civil 3D
AU2011 Speaker::: CI4252: Create Subassemblies That Think Outside the Box With Subassembly Composer for AutoCAD® Civil 3D®
