PuTTY or MobaXterm shows "Unable to use key file" when I use a PEM key

Problem

On Windows, when you try to SSH using a .pem key in PuTTY or MobaXterm, the client doesn't recognize the key.

Cause

PuTTY-family clients use .ppk key files, not .pem.

Solution

1) Convert PEM → PPK

1. Open PuTTYgen (bundled with PuTTY as puttygen.exe).

2. Import the PEM file

   Conversions → Import Key → select elice-cloud-ondemand-xxxx.pem

3. Save as PPK

   Save private key → elice-cloud-ondemand-xxxx.ppk

4. Configure PuTTY or MobaXterm

Field	Value
Host	central-01.tcp.tunnel.elice.io
Port	the port shown in the console
SSH Key	the .ppk file you generated

"Couldn't load private key" error

Cause

The existing PEM file may be in a format PuTTY doesn't recognize.

Solution

1. Back up the original

   copy C:\path\key.pem C:\path\key.orig.pem

2. Convert the PEM format

   ssh-keygen -p -m PEM -f C:\path\key.pem

3. Try Import Key again in PuTTYgen.

It's asking me for a new passphrase

Solution

Don't enter anything — just press Enter twice. → The existing key is kept as-is; only the PEM format is converted.