I make up a few DSTT carts for friends and family and can easily get around 20 ROM's on a 2GB Sandisk Micro SD. I've never encountered the issue you seem to be having either with YSMENU or TTMENU.
It sounds like your MicroSD, Try re-formatting it using Panasonic SD Formatter (Grab it via a Google search) and once you have it, format your card using the following options: FORMAT TYPE - FULL (Erase ON) : FORMAT SIZE ADJUSTMENT - ON (Credit to RetroGameFan for that information)
Oh and you may want to back your GAMES folder up before you format. Afterwards, grab the latest RGF 6.46 Firmware from
HERE and copy the menu you want (YSMENU or TTMENU) to the root of your card.
Formatting usually fixes most issues, however if it still dosn't work, i'd look into the type of SD card your using, Its well known that cheap imitations cause problems.