Issue with downloading Cisco IOS Configs

I've got about 8 switches out of 253 which are not downloading their configs.

When I've looked at the issue and tried to do a manual download I get the following error message Input string was not in a correct format

When I look at the credential login details it just shows Device Template: Cisco IOS-1.3.6.1.4.1.9 and nothing else.

I've checked the switches and I can login to them successfully using the credentials supplied in NCM so not sure why Its not working.

The switches are all Cisco 2950's on the same IOS version, but I have other 2950's on the same IOS version that are working perfectly fine.

Any help would be much appreciated.

Thanks

Jon