I guess you mean you have generated image files from other bluechart MS versions/PC installs which also don't work in your 440s, and i assume you have unlocked the images correctly. As it's a chartplotter made primarily to use Bluecharts it seems that the problem may be elsewhere in that case. Perhaps the SD card adapter or the SD reader of the unit is at fault. Try spraying some dedicated Electrical Contact Cleaner [don't use WD40 or similar!] on the SD adapter contacts internally and externally then thoroughly dry them, or try another adapter if you have one. If that doesn't work, spray the ECC into the unit's card slot and work the SD card in and out a few times. Do this with the unit off, don't over-wet it and don't turn the unit on until the slot has completely dried out.