vim "modifiable" is off

Ok, this may not be the most informed answer as I barely have a working knowledge of vim or linux, But I have found to solution to my problem and it may work for you to. To be specific, My problem was twofold:

1) whenever i tried to edit something in this new file i created, i got the Cannot make changes, 'Modifiable' is off error and...

2) after running :set modifiable and trying to save, i would get an e382 error of 'cannot write, buftype is set. so i couldn't save.

After pouring throuch scads of useless cryptic documentation i figured out this:

1) find the .vimviews directory, for me it was at the root of my git repository, do an

ls 

inside it. i got something like this:

~=+www-halo=+test=+lib=+Halo=+Return2=+HeaderTest.php=
~=+www-halo=+test=+lib=+Halo=+Service=+LandmarkTest.php=
~=+www-halo=+test=+lib=+Halo=+Transaction=+AuthnetTest.php=

Which is totally useless to you since you have a different file structure. but look for the file that is giving you the problem. (oh btw, these are in fact file names, which is completely not obvious by looking at them). find the one that has the file in question and delete that sucker: example:

rm ~=+www-halo=+test=+lib=+Halo=+Return2=+HeaderTest.php=

Problem solved.

I am not familiar with NERDTree but I guess that by typing a in a NERDTree view, it is interpreted as "I want to append something to the NERDTree buffer", but that buffer is not modifiable.

You can check out this answer vim and NERDTree extension - adding a file which explains how to add a file with NERDTree.

This worked for me:

:set buftype=
:w

:set ma

which is short for

:set modifiable

will make a buffer modifiable. And

:set noma

does the opposite.