FrontEndUser strange error

[1dMN]

Hi all.
I installed the "trinity" FEUsers/CustomContent/SelfReg on my 0.12.2 version.
I creted a lot of properties for the registration form, and then I added a group called temp under FEU Managent.
So I put {cms_module module=SelfRegistration group=temp} in my registration page.
All properties seemed ok (someone required, someone optional), but after filling in all fields up to selfregister myself, this is what I see:

Warning: fgets(): supplied argument is not a valid stream resource in /cmssite/modules/FrontEndUsers/FrontEndUsers.api.php on line 761

Fatal error: Call to undefined function: lang() in /cmssite/modules/FrontEndUsers/FrontEndUsers.api.php on line 767.

Well, CMSmailer works in SMTP mode, and all parameters are ok.
What's the problem?!?

Thank you very much for your help.