Hi Edil,
Support for the 7975G was not added until the release of CCM 4.2(3)sr2b as shown below. So, you would need to upgrade to at least that version. There are many bug fixes for 4.2(3) in these newer versions as well;
7975G Call Control compatibility
Supported in Cisco Unified Communications Manager Versions 4.1(3)sr5b, 4.2(3)sr2b, 4.3(1), 5.1.1(b), 5.1(2), 6.0(1) and greater
Supported in Cisco Unified Communications Express and SRST Version 4.1
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6788/phones/ps379/ps8538/product_data_sheet0900aecd8069bdb7.html
Here is the path in the Voice Software downloads to the newer 4.2(3) SR's
Voice and Unified Communications > Cisco Unified CallManager Version 4.2 > Unified Communications Manager Updates > 4.2(3)
Hope this helps!
Rob