Hi!
I am using dhtmlxtree V1.6 professional version. I lock the tree every time the nodes of the tree are in edit mode and release the lock once the changes are saved or canceled.
function lockTree(){
try
{
if (busy) {
tree.lockTree(false);
busy = false;
alert(“Unlock Tree”);
} else {
tree.lockTree(true);
busy = true;
alert(“Lock Tree”);
}
}catch(e){
alert("Error locking tree in edit mode: " + e);
}
}
My problem is the lock tree works for the first time to lock and unlock but after that it doesnt lock any more the tree or if it is locked, doesnt unlock. I was trying to understand the problem for sometime. Today i realized that even the lock example that i downloaded (dhtmlx.com/docs/products/dhtmlxTree/index.shtml) from the website doesnt work: (locks for the first time and than it doesnt lock) But the lock-tree sample on the home page works 
Any idea??
NB: i catch an error saying: “Error locking tree in edit mode: Type error: this._TreeLocker.parentNode has no properties”
There was a bug in lockItem functionality , which prevented correct repeating of lockItem command.
The issue was fixed , and latest build available at dhtmlx.com contains updated file.
You can update your codebase to latest build, or just contact us directly at support@dhtmlx.com - we will send you an updated js file, which contains necessary fix.