I wanted to pass along a tip that I discovered while working with the C3745. Hopefully, it will prevent you from falling into the trap that I fell into...
The C3745 uses Compact Flash for it's flash media. There is an internal Compact Flash device (flash:) and an external Compact Flash device (slot0:)
The router can work with these devices when they are formatted in either LEFS (Low End File System) or DOS FAT file system.
If you only have a single IOS image on one of these devices, apparently the router can find the file and load it without any problems, no matter whether the file system is LEFS or FAT.
However, if you put two IOS images on one of these devices, the router will not be able to find the specific image that is configured to be booted if the filesystem is DOS, because ROMMON only understands the LEFS directory structure.
The solution is to format the flash device (flash: or slot0:) using the LEFS filesystem. This will allow you to be able to put multiple IOS images on Compact Flash, and be able to access them from ROMMON.
Please view the attached text file, while describes the steps to follow to accomplish this. The text was too long to post in a forum article.
You can also find more information on cisco.com at the following link:
I hope that you find this tip helpful.