C# - Can't Delete Image File While Using TinyMCE

i am using TinyMCE AND AsyncFileUpload AND an Update Panel After Uploading , i cannot delete the Images while Adding them to tinymce content because it is being used by another process.

lock (this)
{
if (File.Exists(_FILE_HANDLER_))
{
File.Delete(_FILE_HANDLER_);
}
}

Do i have to Dispose TinyMce :: Like This :

tinyMCE.execCommand('mceFocus', false, '<%= TextBox1.ClientID %>');
tinyMCE.execCommand('mceRemoveControl', false, '<%= TextBox1.ClientID %>');