In the image you've attached, it looks like /toolbar is unable to allocate memory because Windows is reporting that there is no memory available. When Windows reports that there is no memory available, there could be several causes, eg. a script that is not freeing memory correctly, or another application that is using available Windows memory, or a bug in mIRC itself where it is not freeing memory in some contexts. You will need to narrow down the issue to establish what is causing this.
