How do I put a tax block on my account so that the non custodial parent can’t file the Child.?

[Lisa995]

You don't have any control over what someone else does on their own tax return, so there is no way for you to block what someone else may do.

File your return with the correct information and you'll need to let IRS work it out on their end.  That non-custodial parent will need to provide a Form 8332 to IRS showing that YOU released the child to them, in order for them to be able to claim that child....if you didn't sign an 8332 for that non-custodial parent, their claim will be denied by IRS.

[VolvoGirl]

If the other person files first and your return rejects you can print and mail your return and the IRS will determine who is able to claim them.

[Carl]

In a nutshell, just file your return and claim the dependent if you are entitled to do so. When the IRS has a situation where a dependent is claimed on more than one return, then all parties claiming the dependent will be audited (by mail). The loser pays back taxes, fines, penalties and late fees.