SQL Server backup fails on disk space error SQL Server 2008 R2 RTM running on Windows 2008 64bit. 

Having problems backing up a single database with the following command

backup database [somedatabase] 
to disk = '\\somehost\d$\BACKUP\somedirectory\some_database.bak'
with compression, init, stats=1


The database backs up just fine for a while

93 percent processed.
94 percent processed.


Then I get an error about diskspace


  Msg 3202, Level 16, State 1, Line 1
  Write on "\somehost\d$\BACKUP\somedirectory\some_database.bak" failed: 1130 (Not enough server storage is available to process this command.)
  Msg 3013, Level 16, State 1, Line 1
  BACKUP DATABASE is terminating abnormally.


This doesn't make any sense because there is over 800GB of available disk space and the backup is using 121GB.

In SQL Server's logs I get this message

Date        9/25/2013 1:04:56 PM
Log     SQL Server (Current - 9/25/2013 12:15:00 PM)

Source      Backup

Message
BackupIoRequest::ReportIoError: write failure on backup device 
'\\somehost\d$\BACKUP\somedirectory\some_database.bak'. Operating 
system error 1130(Not enough server storage is available to process
this command.).


Some information:


Backups are being executed from the server locally and the backup files are being saved to \\somehost which is another server close by.
Both the local and remote hosts have sufficient disk space. 
Compression is on


Any assistance on getting to real cause of these backup failures would be appreciated. 

Thank you

Update 16:48

As of R2, Compression is a backup option on standard. Thank you RLF. Still having the same problem with or without. The only difference is that the backup fails at 18% without compression. Decided to monitor disk space to make sure nothing else was eating up GB during the backup.



As expected, available disk space went down to 600GB while using compression and 400GB without. Disk space never dipped below 400 though.
The error not enough server storage available is misleading.  This is not disk space, but Windows SMB management memory.  Try restarting the target machine (where the backup is being saved), or at least restart the Server service.

See the following Microsoft support link for instructions on potential registry changes that may be necessary at the machine where the backup is being stored. 

http://support.microsoft.com/kb/304101

Also, you might try a search for "Windows Server error 1130" for more info.