execve EPERM

[sele-nium]

I'm debugging a MIPS elf which run another elf with system call, but doesn't run it, when I start the script in DEBUG I got this:

[+] 	0x90138c74: fork() = 0x2ea4
[+] 	vfork(): is this a child process: True
[+] 	Received interrupt: 0x11
[+] 	0x90138c74: fork() = 0x0
[+] 	Received interrupt: 0x11
[+] 	0x90137ff4: rt_sigaction(signum = 0x3, act = 0x7ff3c888, oldact = 0x7ff3c8a8) = 0x0
[+] 	Received interrupt: 0x11
[+] 	0x90139b54: getpid() = 0x512
[+] 	0x90137ff4: rt_sigaction(signum = 0x2, act = 0x7ff3c888, oldact = 0x7ff3c8a8) = 0x0
[+] 	Received interrupt: 0x11
[+] 	Received interrupt: 0x11
[+] 	0x90137ff4: rt_sigaction(signum = 0x3, act = 0x7ff3c888, oldact = 0x7ff3c8a8) = 0x0
[+] 	Received interrupt: 0x11
[+] 	0x90137ff4: rt_sigaction(signum = 0x2, act = 0x7ff3c888, oldact = 0x7ff3c8a8) = 0x0
[+] 	Received interrupt: 0x11
[+] 	0x90137ff4: rt_sigaction(signum = 0x12, act = 0x7ff3c888, oldact = 0x7ff3c8a8) = 0x0
[+] 	Received interrupt: 0x11
[+] 	0x90138a34: execve(pathname = 0x901445e8, argv = 0x7ff3caa8, envp = 0x7ff3cefc) = -0x1 (EPERM) <<<<<<<<<<<<<<<<<
[+] 	Received interrupt: 0x11

The elf is in directory bin of rootfs and has exec permession 755.
How do I understand what the error is? It seems to me that everything is configured correctly.
I'm using the latest dev commit.