Cisco Vlan stops working on cisco 2950.Other vlans work just not vlan 250.

One thing I've seen under these conditions:
The switch vtp mode is not transparent.
The other switches with that vlan are not set to vtp server.

You create your vlan and it works fine. But once you reboot the switch, you lose the vlan configuration you entered on it! The reason is that unless the switch is in transparent mode, it will not store it's vlan information in it's config. You can verify this by typing "show vlan" on the switch and seeing if it has vlan 250 configured or not. If it doesn't, that's your problem.

Set the switch to vtp mode transparent, configure vlan 250 again, and it will stay good.

By default all the switches are configured in Server MODE,
is 2950 switch getting its vlan 250 from another switch? in case you are accessing vlan 250 from another sw this is possibility. in this case VLAN 250 will always be down. You need to make sure that it can listen vlan 250 from neighbor SW. This is only related to this type of setup.

hope this helps

Additional Information.  Vlan 247 was created on the core (vtp server) and shows up immediately on the 2950.  Vlan 250 had been working for months.  Vlan 247 was just a copy of VLAN 250 replacing 250 with 247
vtp stat shows vtp client with the same revision number and timestamp as the core
sh vlan  shows both the 250 and the 247 domain

I see no differences between vlan 247 and vlan 250
interface Vlan247
 description public vlan
 ip address 192.168.247.254 255.255.255.0
 ip helper-address 10.1.1.10

interface Vlan250
 description public vlan
 ip address 192.168.250.254 255.255.255.0
 ip helper-address 10.1.1.10

2950 sh vtp stat
VTP Version                     : 2
Configuration Revision          : 186
Number of existing VLANs        : 78
VTP Operating Mode              : Client
VTP Domain Name                 : XXXXX
VTP Pruning Mode                : Enabled
VTP V2 Mode                     : Enabled
VTP Traps Generation            : Disabled
MD5 digest                      : 0x9E 0x5E 0x94 0xB5 0xE2 0x31 0xFC 0x6B
Configuration last modified by 10.1.1.200 at 5-27-09 06:55:03

4506 show vtp stat
VTP Version capable             : 1 to 3
VTP version running             : 2
VTP Domain Name                 : XXXXX
VTP Pruning Mode                : Enabled
VTP Traps Generation            : Disabled
Configuration last modified by 10.1.1.200 at 5-27-09 06:55:03
Local updater ID is 10.1.1.200 on interface Vl1 (lowest numbered VLAN interface found)

Feature VLAN:
--------------
VTP Operating Mode                : Server
Maximum VLANs supported locally   : 1005
Number of existing VLANs          : 78
Configuration Revision            : 186


I have not deleted and recreated 250, I just can't figure out why it stopped working?

What is the output of "show vlan" on the 2950? Interface vlan250 is a layer 3 configuration. It will not forward any traffic unless the vlan exists at layer 2. "show interface vlan250" would show down/down if the vlan is non-existent.

I hate VTP anyway, I always prefer to set the switch to transparent mode and manually configure whatever vlans I need. I don't like the idea of depending on a remote device for local configuration.

As far as layer 2 operation, I think 2950 will keep one ip active,  just for testing ( do not do this if are in production)
remove vlan 247 from 2950 and add 250 with ip add, See what happens

Could you show the outputs of:
 sh vlan
 sh int <uplink to router/4506> trunk
 show ip int brief
 show int status

Like bsohn said, the 2950 will only allow one SVI (layer 3 Vlan interface) to be active at a time, so your testing may be somewhat skewed, but as for the users not working either, that is hard to explailn from what you have described.  It sounds like either the vlan is being pruned from the trunk or is not configured on teh 2950.  I'm with mike, vtp stinks, I would recommend transparent mode.

easiest solution was to delete all mention of the vlan and the interfaces for the vlan and recreate.  Once I did that it all started working properly.