Make sure the path is correct.
Also, the example at https://www.dosbox.com/wiki/IMGMOUNT says

Z:>mount c "c:\images" Z:>imgmount d "C:\cdimg.cue" -t iso -fs iso Z:>d: D:> […]
Show full quote

Z:>mount c "c:\images"
Z:>imgmount d "C:\cdimg.cue" -t iso -fs iso
Z:>d:
D:>

and you don't have the -fs part in your command.

I checked the path and it is correct, it doesn't look like DOSbox is reading the directory. I also added the -fs part and it still gives me the same answer.

Are you mounting your computer's C: drive as your DOSBox C drive?
It's recommended to mount a folder as your DOSBox C and not your entire C: drive.
If you're mounting your computer's C: drive as your DOSBox C, then you're trying to mount a folder within the DOSBox C drive as your D: drive, which would confuse DOSBox.

If you're mounting C:\Mech2 as your DOSBox C: drive, it's the same problem -- trying to mount a folder within the DOSBox C as the D: drive.

skitters wrote:

Are you mounting your computer's C: drive as your DOSBox C drive?
It's recommended to mount a folder as your DOSBox C and not your entire C: drive.
If you're mounting your computer's C: drive as your DOSBox C, then you're trying to mount a folder within the DOSBox C drive as your D: drive, which would confuse DOSBox.

I am mounting a folder on C entitle DOSgames.
I suppose the problem might be me being and idiot and not realizing D can't be mounted from a folder within DOSbox C. I'll test that out right now.

Update: It works. I had to list the full path from my computer's C and not the C I set within DOSbox.
Thank God, I was pulling my hair out over this one.
Here's the full command I used if anyone is interested:

1imgmount d "C:\DOSgames\MECH2\MECH2_16B.cue" -t iso -fs iso

Glad you figured it out.
Mechwarrior 2 is great.

you should do two Folders :

C:/dosgames

and
C:/images

then mount c:/dosgames as drive C
and C:/images/mech2...... as CD-rom D