pvk2pfx.exe says bad file format

I have read that to create a .PFX file in Windows I have to use this commandline:

pvk2pfx.exe -pvk MyKey.pvk -spc MyKey.cer -pfx MyPFX.pfx

So I started cmd as Administrator and typed this commandline:

"C:\Program Files (x86)\Windows Kits\8.1\bin\x64\pvk2pfx.exe
" -pvk R:\key\mykey.key -spc R:\mycert.crt -pfx R:\MyPFX.pfx
ERROR: Bad file format.
(Error Code = 0x8007000b).

mykey.key is a text file with this content:

-----BEGIN RSA PRIVATE KEY----- MIIEpwIBAAKCAQEAoM98qgIc9LrFDYyzdOb24EZL89QVq0XFiPVVD88qcxcqfqEE
[lines in between omitted for privacy reasons] hLHvj4JisIWkE60CsbQpxZ+LtUL9Nw//DaeiSr4rGkKBwu034b4bLl0PbQ==
-----END RSA PRIVATE KEY-----

mycert.crt is also a text file with this content:

-----BEGIN CERTIFICATE----- MIID0jCCArqgAwIBAgIMIhKlAG2UZQBuMQwAMA0GCSqGSIb3DQEBCwUAMHIxCzAJ
[lines in between omitted for privacy reasons]
Gg7Vc/CrJWHT42FKT6CLKHEdcLjJYA==
-----END CERTIFICATE-----

I was also prompted for a password.

Windows 7 x64 SP1

So why does pvk2pfx.exe say "bad file format" and how can I create the pfx file from these two files?