I am unaware of any Garmin MapSource product titled “Streets and Roads.” Are you referring to City Navigator or Metro Guide North America? Microsoft has a product called Streets&Trips. The maps from the Microsoft product are not recognized by your Garmin gps.
If you want to use a mapping product in a Garmin gps, with few exceptions in must be a Garmin MapSource product. I assume that you loaded another manufactures products on a micro SD card, but your gps unit will not recognize it. The bargain "other guys product" may not be a bargain in the long run. I have a couple mapping products from other manufactures that will transfer waypoints, and tracks, but will not transfer maps.
A while back I posted how to load Garmin MapSource products on a Garmin gps unit. Just change the name to you Garmin MapSource product and you should be okay. I am sure there are a few hacks around for loading other products, but that is beyond me.
http://www.gboreloaded.com/forums/index.php/topic,120949.0.htmlIf Streets and Roads is not a Garmin MapSource product it maybe creating a conflict. If both products are Garmins I suggest you call Garmin Support. There is a toll free number on their webpage. It may take twenty minutes before you get to talk to a customer service person. But once you have them they are helpful.