Can't open a connection to site 'SYB_BACKUP'. See the error log file in the ASE boot directory.

Resolution--
 Make sure that the sybase backup server is running

and 

2. Verify that the srvnetname for the SYB_BACKUP matches the name created for the backup server in Sybase.
From Isql
1> select * from master..syssevers
2> go

If there is a mismatch, update the name by using sp_dropserver and sp_addserver if necessary

1> sp_dropserver SYB_BACKUP
2> go

1> sp_addserver SYB_BACKUP, null, SERVERNAME_BS
2> go

*Where SERVERNAME_BS is the network name of sybase backup server

For example--

1> select * from sysservers
2> go
 srvid  srvstatus srvname                        srvnetname                       srvclass srvsecmech                     srvcost srvstatus2 
 ------ --------- ------------------------------ -------------------------------- -------- ------------------------------ ------- ---------- 
      1         8 SYB_BACKUP                     SYB_BACKUP                           NULL NULL                              NULL       NULL 
      2      1024 SYB_EJB                        EJBServer                              10 NULL                              NULL       NULL 
      0         9 INBLRL3855                     INBLRL3855                              0 NULL                                 0          0 
      3         9 INBLRL3855_XP                  INBLRL3855_XP                          11 NULL                              1000          0 
      4         9 SYB_JSAGENT                    INBLRL3855_JSAGENT                      7 NULL                              1000          0 
      5         9 loopback                       INBLRL3855                              7 NULL                              1000          0 
      6         8 SYB_JSTASK                     INBLRL3855                              7 NULL                              1000          0 

(7 rows affected)
1> sp_dropserver SYB_BACKUP
2> go
Server dropped.
(return status = 0)
1> sp_addserver SYB_BACKUP, null,INBLRL3855_BS
2> go
Adding server 'SYB_BACKUP', physical name 'INBLRL3855_BS'
Server added.
(return status = 0)
1> exit

D:\sybase_test_database\ASE-15_0\install>isql -Usa -P -SINBLRL3855 -w9999
1> load database dxpo from "compress::D:/sybase_test_database/dxpo_dump_4"
2> go
Backup Server session id is:  8.  Use this value when executing the 'sp_volchanged' system stored procedure after fulfilling any volume change request from the Backup Server.
Backup Server: 4.132.1.1: Attempting to open byte stream device: 'compress::D:/sybase_test_database/dxpo_dump_4::00'
Backup Server: 6.28.1.1: Dumpfile name 'dxpo140540972D   ' section number 1 mounted on byte stream 'compress::D:/sybase_test_database/dxpo_dump_4::00'
Msg 3105, Level 16, State 1:
Server 'INBLRL3855', Line 1:
Data on dump will not fit into current database. Need 17380 Mbyte database.
1> sp_helpdb
2> go
 name           db_size       owner dbid  created      status                                                               
 -------------- ------------- ----- ----- ------------ -------------------------------------------------------------------- 
 dxpo               5120.0 MB sa        5 Feb 18, 2014 select into/bulkcopy/pllsort, mixed log and data                     
 master               13.0 MB sa        1 Feb 03, 2014 mixed log and data                                                   
 model                 3.0 MB sa        3 Feb 03, 2014 mixed log and data                                                   
 pubs2                 4.0 MB sa        6 Feb 19, 2014 trunc log on chkpt, mixed log and data                               
 sybmgmtdb            75.0 MB sa        4 Feb 03, 2014 select into/bulkcopy/pllsort, trunc log on chkpt, mixed log and data 
 sybsystemdb           4.0 MB sa    31513 Feb 03, 2014 trunc log on chkpt, mixed log and data                               
 sybsystemprocs      132.0 MB sa    31514 Feb 03, 2014 trunc log on chkpt, mixed log and data                               
 tempdb                4.0 MB sa        2 Feb 27, 2014 select into/bulkcopy/pllsort, trunc log on chkpt, mixed log and data 

(1 row affected)

(return status = 0)

sybase:CREATE or ALTER DATABASE failed because the device 'default' has no space available either for log or for data.

When this error start showing you that means you don't have space to be utilized by DB for data storage or even for log purpose. so you can't alter database size.

You need to initialize some spare disk.

i.e.

1> disk init name=sybase_disk,physname="D:\sybase_test_database\data\sybase.dat",skip_alloc="true",size="10G"