Event ID: 18272 errors when running a backup.

We are running a SQL Backup job at 1:00 in the morning but we get the following Event ID: 18272 This previously worked fine but only started in the last couple of days.


Log Name: Application
Source: MSSQLSERVER
Date: 2014/06/11 05:20:18 AM
Event ID: 18272
Task Category: Backup
Level: Error
Keywords: Classic
User: MURZA\*********
Computer: ********.murza.co.za
Description:
During restore restart, an I/O error occurred on checkpoint file 'G:\SQL Backup\RestoreCheckpointDB15.CKP' (operating system error 1784(failed to retrieve text for this error. Reason: 15105)). The statement is proceeding but cannot be restarted. Ensure that a valid storage location exists for the checkpoint file.
Event Xml:
<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event"&gt;
<System>
<Provider Name="MSSQLSERVER" />
<EventID Qualifiers="49152">18272</EventID>
<Level>2</Level>
<Task>6</Task>
<Keywords>0x80000000000000</Keywords>
<TimeCreated SystemTime="2014-06-11T03:20:18.000000000Z" />
<EventRecordID>481159</EventRecordID>
<Channel>Application</Channel>
<Computer>********.murza.co.za</Computer>
<Security UserID="**********" />
</System>
<EventData>
<Data>G:\SQL Backup\RestoreCheckpointDB15.CKP</Data>
<Data>1784(failed to retrieve text for this error. Reason: 15105)</Data>
<Binary>60470000100000000F0000005A0041005200490056004D00550052002D00530051004C0030003100000000000000</Binary>
</EventData>
</Event>



Does anyone know what causes this, on online forums they all say I must log a call with redgate software.

I also can't seem to find a network or san issue causing this.

Please help