ERROR: Dropbox API: (500) Internal Server Error

Why does it always happens on the first try but on the second try the backup file was able to upload successfully.

[12-Apr-2015 23:39:02] Compressing files as ZipArchive. Please be patient, this may take a moment.
[12-Apr-2015 23:40:42] Restart after 101 seconds.
[12-Apr-2015 23:42:24] Restart after 101 seconds.
[12-Apr-2015 23:44:12] Restart after 107 seconds.
[12-Apr-2015 23:46:06] Restart after 112 seconds.
[12-Apr-2015 23:53:18] WARNING: Job restarts due to inactivity for more than 5 minutes.
[12-Apr-2015 23:53:18] 2. Trying to create backup archive …
[12-Apr-2015 23:55:21] Restart after 123 seconds.
[12-Apr-2015 23:57:15] Restart after 113 seconds.
[12-Apr-2015 23:59:39] Restart after 144 seconds.
[13-Apr-2015 00:00:10] Backup archive created.
[13-Apr-2015 00:00:10] Archive size is 511.76 MB.
[13-Apr-2015 00:00:10] 13318 Files with 1.50 GB in Archive.
[13-Apr-2015 00:00:10] Restart will be executed now.
[13-Apr-2015 00:00:13] 1. Try to send backup file to Dropbox …
[13-Apr-2015 00:00:15] Authenticated with Dropbox of user Catco
[13-Apr-2015 00:00:15] 827.89 MB available on your Dropbox
[13-Apr-2015 00:00:15] Uploading to Dropbox …
[13-Apr-2015 00:01:51] Restart after 99 seconds.
[13-Apr-2015 00:03:30] Restart after 98 seconds.
[13-Apr-2015 00:04:24] ERROR: Dropbox API: (500) Internal Server Error
[13-Apr-2015 00:04:24] Restart will be executed now.
[13-Apr-2015 00:04:26] 2. Try to send backup file to Dropbox …
[13-Apr-2015 00:04:26] Authenticated with Dropbox of user Catco
[13-Apr-2015 00:04:26] 827.89 MB available on your Dropbox
[13-Apr-2015 00:04:26] Uploading to Dropbox …
[13-Apr-2015 00:06:07] Restart after 101 seconds.
[13-Apr-2015 00:07:16] Backup transferred to https://api-content.dropbox.com/1/files/dropbox/bunbury/bunbury.zip
[13-Apr-2015 00:07:16] One old log deleted
[13-Apr-2015 00:07:16] ERROR: Job has ended with errors in 1694 seconds. You must resolve the errors for correct execution.

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