Cisco Routers :: SRP541w - Values Are Invalid

We purchased a Cisco 541w router for one of our customers.
 
The main reason was to provide them with 3g backup solution for their business.
 
In order for the router to recognise the 3G router the firmware was upgraded SRP540_1.02.01_023_081211_1136.
 
We arrived on site last night to do the install but couldn't make any changes to the already configured router.  Every time we attempted add a vlan or adjust the dhcp scope the router would return "The values are invalid".
 
Worked at this for over 1 hour and then decided to factory reset the router to see if that would revert the router to use the original firmware.
 
This didn't revert to the previous firmware but we magically could now make network changes without problem.
 
So everything was good, we reconfigured the router, tested 3G and failed the wan1 interface back and forth and the customer was very happy.
 
Customer arrived onsite this morning and the router was running on 3G.  Every 8 - 10 minutes it was attempting a failover between connections.
 
I decided to turn off the failover for the time being and investigate further but yet again i was back to "the values are invalid"
 
We've had to pull the router as the customer is about 2hours away and revert back to their BT router.
 
Found this document for another SRP model - A warning message may appear in the Basic Wireless Settings screen with the text “The values are invalid” when modifying the wireless profile. Set the SRP 521W to its default setting (CSCtd49614).
 
[URL]
 
Will firmware SRP540_1.2.4_003_011112_1847 released only 2 days ago cure the problem?