当我点击paypal付款按钮时，会显示以下错误。
为什么会显示此错误？
A PHP Error was encountered
Severity: Warning
Message: error_log(../PayPal.log): failed to open stream: Permission denied
Filename: Core/PayPalLoggingManager.php
Line Number: 116
[Above error repeated 5 times]
A PHP Error was encountered
Severity: Warning
Message: file_put_contents(/var/www/html/system/paypal/lib/PayPal/Cache/../../../var/auth.cache): failed to open stream: Permission denied
Filename: Cache/AuthorizationCache.php
Line Number: 77
Exception: Failed to write cache
( ! ) Fatal error: Call to undefined method Exception::getData() in /var/www/html/application/controllers/cart.php on line 1695
Call Stack
# Time Memory Function Location
1 0.0000 239624 {main}( ) .../index.php:0
2 0.0003 392832 require_once( '/var/www/html/system/core/CodeIgniter.php' ) .../index.php:204
3 0.0068 1541016 call_user_func_array:{/var/www/html/system/core/CodeIgniter.php:359} ( ) .../CodeIgniter.php:359
4 0.0068 1544352 Cart->paypal_payment( ) .../CodeIgniter.php:359