When you power on a VM with 128GB RAM and no memory reservations ESXi creates a 128GB swap file. Most probably you don't have 128GB space available left on the datastore.
If this is the case your options are:
- Reduce VM memory size (probably not what you want)
- Add disk space to datastore (probably not available)
- Configure a memory reservation (if ESXi really has enough RAM I'd do this)
- Configure a different swap location (but then you need that disk space somewhere else)
If memory is reserved then no swap file is needed because memory is reserved. In that case if 128GB RAM aren't available then you can't power on the VM. Which isn't actually much different from the current situation