ASP.NET Webservice Query MSSQL Timeout (Poolgrösse/Poolsize)

I created a new webservice where I want to get some SQL queries. It worked for a while but sometimes I get the following error:

System.InvalidOperationException: Timeout abgelaufen. Das Zeitlimit ist vor dem Anfordern einer 
Verbindung aus dem Pool abgelaufen. M&#246;glicherweise werden alle Verbindungen im Pool bereits 
verwendet, und die maximale Poolgr&#246;&#223;e wurde erreicht.
bei System.Data.ProviderBase.DbConnectionFactory.TryGetConnection(DbConnection owningConnection, 
TaskCompletionSource`1 retry, DbConnectionOptions userOptions, DbConnectionInternal oldConnection, 
DbConnectionInternal& connection)
bei System.Data.ProviderBase.DbConnectionInternal.TryOpenConnectionInternal(DbConnection 
outerConnection, DbConnectionFactory connectionFactory, TaskCompletionSource`1 retry, 
DbConnectionOptions 
userOptions)
bei System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry)
bei System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry)
bei System.Data.SqlClient.SqlConnection.Open()
bei SailTrainer.GetSchueler(String un) in C:\inetpub\wwwroot\alert\App_Code\SailTrainer.vb:Zeile 81.

after a while it just work again.

Any of you an idea?

Edit

I tried con.Close() at the start of the function that it closes already open connection before opening a new one but that doesn't seem to work.

and every time I save my .asmx file it works fine again for a few queries.

Solution

Here is another disgussion:

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