One of my servers says the software is expired + error

Problem one,
I thought it was odd that I wasn't able to enter our registration key anywhere, but now one out of the three servers that I installed SQL Backup to is marked as expired. All three versions are version 4.1.0.207. I had tested the software on the server that is having the expiration issue but had uninstalled that version and reinstalled the latest version when we purchased the software recently. I used the same install to install all three servers. None of them asked me to register the software which I thought very odd.

Problem two,
On another server, I'm able to backup 2 databases but not any more than that. All the others yield this error code:
From: SQLBackup@DTNSQL16 [mailto:SQLBackup@DTNSQL16]
Sent: Tuesday, March 07, 2006 1:15 AM
To: Leslie, Linda
Subject: ERROR - full backup [multiple databases] on 3/7/2006 1:15:03 AM

SQL Backup log file
3/7/2006 1:15:01 AM: Backing up sqlcompliance_dtnsql16 (full database) to:
\\DTNBCK500\DTNSQL16 Backups\sqlcompliance_dtnsql16.sqb

3/7/2006 1:15:01 AM: BACKUP DATABASE [sqlcompliance_dtnsql16] TO DISK = '\\DTNBCK500\DTNSQL16 Backups\sqlcompliance_dtnsql16.sqb' WITH NAME = '<AUTO>', DESCRIPTION = '<AUTO>', INIT, MAILTO = 'lleslie@plls.com', COMPRESSION = 1, THREADS = 1

3/7/2006 1:15:02 AM: Thread 0 error:
Error 620: Error writing to backup file(s).
Process terminated unexpectedly. Error code: -2139684860
Thread 0 warning:
Warning 210: Error writing to backup file: \\DTNBCK500\DTNSQL16 Backups\sqlcompliance_dtnsql16.sqb
Warning: System error code: (The operation completed successfully)

3/7/2006 1:15:03 AM: Server: Msg 3013
BACKUP DATABASE is terminating abnormally.
3/7/2006 1:15:03 AM: Server: Msg 3202
Write on 'SQLBACKUP_F8B73BC9-ADC6-47AF-9266-EB9C16B07637' failed, status = 112. See the SQL Server error log for more details.

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There is plenty of space on the server and I tried changing the location and this didn't help. Any ideas?
Thanks,
Linda
Premier Lease & Loan Services