CodeIgniter checkboxes

I have this code which shows 10 sets of checkboxes and 1 want only 1 set of checkboxes can be checked at a time and then sent to database. but errors show when i leave other set of checkboxes unchecked. It says Severity: Warning

Message: implode(): Invalid arguments passed

and

column field cannot be null. pls help this is my first question here hope someone can help

Please check the following boxes related to end-user's role: Requestor:
Purchase Request/Service Request
Work Order Planning, Process and Plant Performance:
Planner (Mech, Elec, I&C and Process Engr.)
Planning Head Approver:
Site Approver (Plant Manager/Deputy GM)
VP, SVP, CFO, EVP, President Finance Accounting and Budget:
AP Officer
Inventory Accountant/Controller
Budget Officer Procurement:
Procurement Staff/Encoder
Buyer
SPO-Site Procurement Officer
Materials Management Head Management Information System:
MIS ICT
MIS SYSDEV Warehouse: Receiving and Inventory Issuances:
Warehouse Store-man
Warehouse Supervisor Internal Audit:
Intra-Company Audit Team
Work Management:
Requestor-Work Order(Operations)
Servicing Group: Mech, Elect, GSU, I&C, PDG Accreditation and Fuel Management:
Accreditation Officer
Fuel Manager/Staff