It seems Ubuntu sees the small SSD and big HDD set in RAID and cannot install Ubuntu side by side without disabling the RAID. See Only 'sdb' shows up when installing 12.04 on a new Dell inspiron 14z.
I am not sure why WUBI install didn't work at first. Changing the NTFS partition to ext4 was a mistake. WUBI install does not use the partition directly but uses a large file inside a Windows partition (NTFS). This is why one can use WUBI install without making any new partition. The installation will put the big file in C: by default. Since Windows cannot read/write ext4 (or any other Linux partition) WUBI cannot use these types of partitions. Remember WUBI installations is done from within Windows.
First, Boot Windows and uninstall WUBI installation using Windows Uninstall feature.
- Boot from USB stick and select "Try Ubuntu"
- Open a terminal by pressing
Ctrl+Alt+T and enter
-E -r /dev/sda.
- Using Gparted delete the ext4 partition you had created before. Default side-by-side Ubuntu install should create all the partitions it needs on its own.
- Start the Install Ubuntu process as before.
Once the RAID is removed you should get the "alongside" option. However, you may choose "something else" and use the small SSD for the
/ partition and the the HDD for
/home and swap. See Is it safe to install the / partition on an SSD?