SWFupload500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