Error: module ctype is in file 'std/ctype.d' which cannot be read - when running dmd

[Roman via Digitalmars-d-learn]

I've just tried to compile a program with `rdmd`, but get the 
following error:

     count_words.d(1): Error: module ctype is in file 
'std/ctype.d' which cannot be read
     import path[0] = .
     import path[1] = 
/home/roman/dlang/dmd-2.071.0/linux/bin64/../../src/phobos
     import path[2] = 
/home/roman/dlang/dmd-2.071.0/linux/bin64/../../src/druntime/import

The error is due to the `import std.ctype` statement that I have. 
If I remove everything else from the file and leave just that, 
the error persists, so it's clearly the only reason why I'm 
getting this error.

A quick Google search led me to this old thread: 
http://forum.dlang.org/thread/imn3fg$2nve$1@digitalmars.com, 
however it seems the issues wasn't resolved for that person. It 
looks like I'm having the same issue.

To further explain the situation:

1. I'm on Ubuntu 16.04

2. I've installed D with the installation script `curl -fsS 
https://dlang.org/install.sh | bash -s dmd` from here 
https://dlang.org/download.html

3. I've followed the installation script suggestion and ran 
`source ~/dlang/dmd-2.071.0/activate`

4. Both dirs that show up in the error output do exist and 
contain files and other dirs. I haven't changed anything, the 
installation script put it there.

And it doesn't work. Would appreciate any help.