Query from a form-Runtime Error 3211

[RaunLGoode]

I am trying to shorten a long list of Employees with a build table query that interrogates table tblActCont creates tblACxGL with only the active contractors assigned to a specific group leader.

In Query qryACxGL I have three fields:
GrpLead, EmpName and Emp#

In the GrpLead field of qryACxGL I have the following criteria:
[Forms]![frmTask]![txtGrpLead]

I would then fill txtGrpLead in frmTask with a value and test the query from the query and from frmTask, using a command button and the On Click Event. Initially it worked just fine.
Next I created using a combo box from tblActGrpLead and changed the query criteria to:
[Forms]![frmTask]![cboGrpLead]
Now when I run the query I get this error:
Run-time error ‘3211’:
The database engine could not lock table ‘tblActiveContractors’ because it is already in use by another person or process.

I have tried using a combo box to fill txtGrpLead After Update and went back to the original Criteria:
[Forms]![frmTask]![txtGrpLead]
I still get Run-time error ‘3211’….

I worked on this all weekend. Can somebody tell me what I am doing wrong or tell me a better way to do this