I tried a clean install like you said letting forge get mcp with no custom code in and it still gave me the error.
Here is a pastebin of the install and attempted recompile http://pastebin.com/H7FUWKDS.
Here's the last few lines:
=============================== Minecraft Forge Setup Finished =================================
static-107:forge 2 joshuac$ cd mcp/
static-107:mcp joshuac$ ./recompile.sh
== MCP 7.23 (data: 7.23, client: 1.4.5, server: 1.4.5) ==
# found ff, ff patches, srgs, name csvs, doc csvs, param csvs, renumber csv, astyle, astyle config
== Recompiling client ==
> Cleaning bin
> Recompiling
- Done in 18.85 seconds
!! Can not find server sources, try decompiling !!
static-107:mcp joshuac$