So, I have downloaded the most recent version of BLT. For some reason, though, trying to update mods I downloaded doesn't work, as their status always gets stuck on "verifying." I am not able to download anything off of the paydaymods site, as a long list of errors appears that looks like this:

An uncaught Exception was encountered
Type: Exception

Message: Session: Configured save path '/var/www/payday_manage/session_data' is not writable by the PHP process.

Filename: /var/www/payday_manage/system/libraries/Session/drivers/Session_files_driver.php

Line Number: 124

Backtrace:

File: /var/www/payday_manage/application/models/Users.php
Line: 176
Function: library

File: /var/www/payday_manage/application/models/Mods.php
Line: 374
Function: model

File: /var/www/payday_manage/application/controllers/Download.php
Line: 24
Function: getModFromId

File: /var/www/payday_manage/index.php
Line: 292
Function: require_once

A PHP Error was encountered
Severity: Warning

Message: fopen(426db82a3ea3b56d132a1889fc2a5e9e405b14fd): failed to open stream: Permission denied

Filename: drivers/Session_files_driver.php

Line Number: 156

Backtrace:


I can download mods off of Mod Workshop, and the override ones work fine, but the normal mods I have downloaded cannot be used with the latest version of BLT and need to be updated by their creators. What do I do?