Quote Originally Posted by VaZso
The post-boot file is executable.

Now it contains only:
/usr/local/no-ip/noip2

If I launch it, the no-ip is starting to run.

If I modify the post-boot to:
#!/bin/sh
/usr/local/no-ip/noip2

Then it says:
-sh ./post-boot: not found

What would be the problem?
It looks as if /bin/sh is not executable. As far as I can tell, and as strange as it sounds, it's the only explanation. Could you try
Code:
/bin/sh
ls -l /bin/sh
ls -lL /bin/sh
mount
and post the results ?