Cannot find Joomla XML installation file and path during installation

I need to export data from my old Joomla 3.0.3 site to the new 3.7.5 site. When installing the vData package on my 3.0.3 site I get the error saying that 'Cannot find Joomla XML installation file' and further that 'installation path not found' and 'error when installing com_vdata.zip'.

Also when trying to install to the new 3.7.5 site I get the error saying 'unable to write entry' and 'error when installing com_vdata.zip'.

vData version is 2.9.12

Hello,
Are you able to install other extensions on the same website? Please redownload vData from WDMtech website and try to install again. If you still find the error, Please share your backend & FTP login credentials via Contact us form, We'll look into it.

I downloaded the package again from WDMtech website. Didn't work for my old Joomla 3.0.3 site. It says JFolder: :files: Path is not a directory. Path: /home/int27824/public_html/tmp/install_59a43303de108

Could it be because my new Joomla 3.7.5 test installation is a subdirectory of the old site? According to Joomla it should work that way as well. I added the new site's database tables to the existing old database. Joomla 3.0.3 site backend can be accessed at discoverit.fi/administrator/index.php?L_08n_k17=A_23e_N01

Credentials:
username: jarkkari
password: P_t13_K_2

Warm regards,
Kai

Can you delete my earlier answer after getting the credentials? I accidentally sent them together with the reply?

I removed the new Joomla 3.7.5 test installation directory and changed the back-end access credentials. Now the vData installation goes through but I just get a source code page in the browser after 1st time authentication.