SWFupload 500异常

SWFupload 500错误
discuz 论坛将www域名换成bbs后编辑器内swfuplaod上传报500错误，但是有时候能正常上传;
目前基本排除服务器上PHP的问题，因为改成空白页面也一样报错。
有人遇到过这个问题吗？求指点


swfupload 日志：

---SWFUpload Instance Info---
Version: 2.5.0 2010-01-15 Beta 2
Movie Name: SWFUpload_0
Settings:
upload_url:               http://bbs.xxxx.com/misc.php?mod=swfupload&action=swfupload&operation=upload&fid=72
flash_url:                static/image/common/swfupload.swf?preventswfcaching=1398395968643
flash9_url:                static/image/common/swfupload.swf?preventswfcaching=1398395968643
use_query_string:         false
requeue_on_error:         false
http_success:             
assume_success_timeout:   0
file_post_name:           Filedata
post_params:              [object Object]
file_types:               *.jpg;*.jpeg;*.gif;*.png
file_types_description:   Image File
file_size_limit:          5000
file_upload_limit:        0
file_queue_limit:         0
debug:                    true
prevent_swf_caching:      true
button_placeholder_id:    imgSpanButtonPlaceholder
button_placeholder:       Not Set
button_image_url:         /static/image/common/uploadbutton.png
button_width:             100
button_height:            25
button_text:              
button_text_style:        color: #000000; font-size: 16pt;
button_text_top_padding:  0
button_text_left_padding: 0
button_action:            -110
button_cursor:            -2
button_disabled:          false
custom_settings:          [object Object]
Event Handlers:
swfupload_preload_handler assigned:  true
swfupload_load_failed_handler assigned:  true
swfupload_loaded_handler assigned:  false
mouse_click_handler assigned:       false
mouse_over_handler assigned:        false
mouse_out_handler assigned:         false
file_dialog_start_handler assigned: true
file_queued_handler assigned:       true
file_queue_error_handler assigned:  true
upload_resize_start_handler assigned:      false
upload_start_handler assigned:      true
upload_progress_handler assigned:   true
upload_error_handler assigned:      true
upload_success_handler assigned:    true
upload_complete_handler assigned:   true
debug_handler assigned:             true
Support:
Load:                     Yes
Image Resize:             No

SWF DEBUG: SWFUpload Init Complete
SWF DEBUG: 
SWF DEBUG: ----- SWF DEBUG OUTPUT ----
SWF DEBUG: Version:                2.5.0 FP9 2010-02-17 Beta 3
SWF DEBUG: movieName:              SWFUpload_0
SWF DEBUG: Upload URL:             http://bbs.xxxx.com/misc.php?mod=swfupload&action=swfupload&operation=upload&fid=72
SWF DEBUG: File Types String:      *.jpg;*.jpeg;*.gif;*.png
SWF DEBUG: Parsed File Types:      jpg,jpeg,gif,png
SWF DEBUG: HTTP Success:           0
SWF DEBUG: File Types Description: Image File (*.jpg;*.jpeg;*.gif;*.png)
SWF DEBUG: File Size Limit:        5120000 bytes
SWF DEBUG: File Upload Limit:      0