Additionally
Enable files extensions in Windows to see if it's not named gmapsupp.img.img, sometimes it happens-
Check with gmaptool if the map in sd is really unlocked
[Only registered and activated users can see links. ]
Drag the img in gmaptool and hit Details tab, in log you'll see if it's locked-
example of a locked map log:
/gmap3d.img, length 192499712
Header: 04.10.2012 10:16:47, DSKIMG, XOR 00, V 20.13, Ms 0, D236411AG000
Mapset: CN North America NT 2013.30 3D
fat: 1000h - 1200h - 25000h, block 4096
maps: 141, sub-files 141

Sub-file fat length
I10FE49D GMP 1200h 4894248
GMP: TRE RGN LBL
map 10fe49d (17818781)
PID 1, FID 2775, region 1,1
PID 1, FID 2775, region 1,3
PID 1, FID 2775, region 1,4
PID 2, FID 2775, region 1,11
date 04.10.2012 09:41:06
priority 30, parameters 1 3 17 3, locked, transparent
N: 21.718941, S: 21.251378, W: -158.290758, E: -157.647243
CN North America NT 2013.30 3D
Copyright 1995-2012 by GARMIN Corporation.
CP 1252, Western European Corrected
Bitmaps 100, size 3948392 (4)
Use "Map" folder in sd root and rename the map anyname.img (CNEU.img for example)
"Map" is with big M (capital letter) and shouldnt support gmapsupp.img naming.
Garmin folder supports gmapsupp.img naming. Probably one gmapsupp.img per Garmin folder.