We are currently considering changing to iBGP on our network but can I ask will OSPF error's ( like new master flag=false, malformed init mesage, reject, ......) impact the same on iBGP?

Yes, OSPF (or any IGP) is needed to provide loopback reachability for an iBGP AS so issues in OSPF that cause routes to flap can affect BGP and cause the peerings go down.

If the network is well built and designed, this shouldn't happen very often.

Ok - next question is re-adjacency – with OSPF can take up to 5mins will iBGP be the same

Ok - next question is re-adjacency – with OSPF can take up to 5mins will iBGP be the same

How many routes and routers do you have and what OSPF network types are you using - boradcast, point-to-point, etc?

Presently L2 bridged because 5min re-adjacency with OSPF was just too long for customers which they noticed and complained?
so now OSPF is used for management and L2 bridged for client PPPoE?

Ok - next question is re-adjacency – with OSPF can take up to 5mins will iBGP be the same

How many routes and routers do you have and what OSPF network types are you using - boradcast, point-to-point, etc?

We have just short of 800 routes with over 60 routers, ospf type is mostly PTP

Ok - next question is re-adjacency – with OSPF can take up to 5mins will iBGP be the same

How many routes and routers do you have and what OSPF network types are you using - boradcast, point-to-point, etc?

We have just short of 800 routes with over 60 routers, ospf type is mostly PTP

Then your answer is no, the convergence time for OSPF by default is 40secs, which means that your network can be reachable again in less than a minute or like 3-4 ICMP replies, if you're using the default BGP timeout / keepalive you're going to need like 180secs of no communication before the BGP session goes down, but just to be clear, your entire network depend on the IGP & EGP to keep working normal, if one of those fails you're going to experiment intermittences & outages in your network

Many thanks for replies - So as i understand
(1) ...180secs of no communication before the BGP session goes down...
(2) ...convergence time for OSPF by default is 40secs.... how fast is iBGP to recover