Some help needed – I'm kind of a newbie

I’ll try to explain as simple as I can. I got the hard task of sorting out someone else’s mess. 2 years old wordpress version was installed and as far as I know without MySQL (cheap hosting) and it used PDO plugin instead. One couldn’t insert any pictures or documents…they would upload but one would just see broken image link. Somehow i managed to update wp to latest version and I also created remote mysql database on my personal hosting to use it with wordpress of the site i’m tring to fix. During wp upgrade it said it needs to update db and than that it was successful (I also changed wp-config to point to database). All that said I still can’t insert images or docs, when I try to insert image I get errors:

Warning: addslashes() expects parameter 1 to be string, array given in /web/d1/users/bralnodr/beta/wp-content/pdo/db.php on line 117

Warning: Cannot modify header information – headers already sent by (output started at /web/d1/users/bralnodr/beta/wp-content/pdo/db.php:117) in /web/d1/users/bralnodr/beta/wp-includes/pluggable.php on line 866

I looked at those lines but have no clue what to do with them. Does anyone have any suggestions? Do i need to delete PDO, is my database linked, are there just a few modifications to be made or should i go to my last resort and do a clean install? Please don’t tell me to ask this site’s hosting company anything because they don’t support mysql, they don’t even have a platform like cpanel or anything, they want written and stamped request send to them by fax for any changes. How lame is that? It’s not like i’m totally new to coding and didn’t try to figure it out myself, please try to help, any tips would be much appreciated. Thank you