Screws Instead of Nails

I have a Decra Stratos roof. Everything was fastened with black coated (about} 7d nails, which have stayed in place over-all on the long flat roof panels. However, the same nails used on the eve 2x6 boards for the10" hip-ridge pieces keep backing out. What type of corrosion coated screw would be compatible with this metal roof as not to cause a metal reaction or what definitely "not" to use. Thank you