it says i do not have enough pipes to do that, yet players have the correct materials and permissions

Have you assigned them a permission level?

yes i have

I'm not sure. Could you send me your config file. 

NullReferenceException: Object reference not set to an instance of an object

  at Oxide.Plugins.SyncPipes+Pipe+Converter.WriteJson (Newtonsoft.Json.JsonWriter writer, System.Object value, Newtonsoft.Json.JsonSerializer serializer) [0x00237] in :0 

  at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeConvertable (Newtonsoft.Json.JsonWriter writer, Newtonsoft.Json.JsonConverter converter, System.Object value, Newtonsoft.Json.Serialization.JsonContract contract, Newtonsoft.Json.Serialization.JsonContainerContract collectionContract, Newtonsoft.Json.Serialization.JsonProperty containerProperty) [0x0008a] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeValue (Newtonsoft.Json.JsonWriter writer, System.Object value, Newtonsoft.Json.Serialization.JsonContract valueContract, Newtonsoft.Json.Serialization.JsonProperty member, Newtonsoft.Json.Serialization.JsonContainerContract containerContract, Newtonsoft.Json.Serialization.JsonProperty containerProperty) [0x00071] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize (Newtonsoft.Json.JsonWriter jsonWriter, System.Object value, System.Type objectType) [0x00079] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.JsonSerializer.SerializeInternal (Newtonsoft.Json.JsonWriter jsonWriter, System.Object value, System.Type objectType) [0x00253] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.JsonSerializer.Serialize (Newtonsoft.Json.JsonWriter jsonWriter, System.Object value, System.Type objectType) [0x00000] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.JsonConvert.SerializeObjectInternal (System.Object value, System.Type type, Newtonsoft.Json.JsonSerializer jsonSerializer) [0x00028] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.JsonConvert.SerializeObject (System.Object value, System.Type type, Newtonsoft.Json.Formatting formatting, Newtonsoft.Json.JsonSerializerSettings settings) [0x0000e] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.JsonConvert.SerializeObject (System.Object value, Newtonsoft.Json.Formatting formatting, Newtonsoft.Json.JsonSerializerSettings settings) [0x00000] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Newtonsoft.Json.JsonConvert.SerializeObject (System.Object value, Newtonsoft.Json.Formatting formatting) [0x00000] in <2ae3f091decd4989b3c4d466e6eb5985>:0 

  at Oxide.Plugins.SyncPipes+DataStore1_0+c__Iterator0.MoveNext () [0x000bb] in :0 

  at UnityEngine.SetupCoroutine.InvokeMoveNext (System.Collections.IEnumerator enumerator, System.IntPtr returnValueAddress) [0x00026] in :0 

What do you mean by the pipes are invisible?

some of the pipes still go invisable

I'm was not aware of pipes going invisible. Do you mean they are not loading in after a restart?

So since update just typing /p gives the message 'You've not got enough pipes to build that I'm afraid.'

Any update on this?

Which update are you referring to? 
Have you granted a permission level? If you put in /p s how many puppies does it say you have? 

Merged post

That should say "...how many pipes does it say you have?"
Wrote it on my phone just realised autocorrect got in the way :S.

I'm getting the same message even though default permission has been granted. The only way to fix it was to grant Admin permission but every now and then, Admin perm auto revokes leaving default perm still granted but getting the message again "You've not got enough pipes to build that I'm afraid".

Also for the first time, a player has informed me that his pipes have disappeared, as in deleted. I've never experienced this on my server though I have on other servers with JPipes.

Have you granted any permission levels to users?
Were the pipes that vanished connected to a quarry?
Granting all users admin is not ideal as it means all pipes are accessible/deletable by all users. 

"Have you granted any permission levels to users?"
My DEV's fixed that now, thank you for pointing it out.

"Were the pipes that vanished connected to a quarry?"
Players Quote:
"They were connected from storage box to storage box. Also lost pipes from Pump Jack to Oil Refinery and back to Pump Jack re-fuel"

"Granting all users admin is not ideal as it means all pipes are accessible/deletable by all users."
I know, It was a tuff decision. Its a PvE server and everybody loves the versatility of SyncPipes so I had to make a call. I just didn't tell them.

There was an intermittent issue with pumpjacks and quarries on server restarts. Not managed to find the cause of this yet as I've not been able to recreate it locally. Not aware of any issues with other containers.

That is the first time I've been made aware of it on my server. I have had them go invisible but that to me is of no consequence to me.
If it occurs again I will be sure to let you know with as much detail as I can muster.
Thank you for your help.
BTW. Fantastic plugin man, hope to see pipes become Barrels in the future.